2-(Anilinomethyl)imidazolines as α1 adrenergic receptor agonists: The discovery of α10 subtype selective 2′-alkylsulfonyl-substituted analogues

Article abstract of DOI:10.1021/jm000542r

A series of 2′-alkylthio-2-(anilinomethyl)imidazolines were prepared to examine the effect of the alkyl group size, sulfur oxidation state, and phenyl ring substitution on ligand binding and agonism of α-adrenergic receptor subtypes α_1a, α_1b, α_1d, α_2a, and α_2c. Binding at all receptor subtypes decreased for compounds in the sulfone oxidation state as compared to their sulfide analogues. While sulfides were generally potent, nonselective agonists, sulfones exhibited α_1a subtype selectivity in a cell-based functional assay. Sulfone (32) was 250-7000-fold selective for α_1a vs all other subtypes.

Full text of DOI:10.1021/jm000542r

J . Med. Chem. 2002, 45, 2229-2239
2229
2-(An ilin om eth yl)im id a zolin es a s r1 Ad r en er gic Recep tor Agon ists: th e
Discover y of r1a Su btyp e Selective 2′-Alk ylsu lfon yl-Su bstitu ted An a logu es
Stephen J . Hodson,* Michael J . Bishop,† J ason D. Speake,† Frank Navas, III,† Deanna T. Garrison,†
Eric C. Bigham,† David L. Saussy, J r.,‡ J ames A. Liacos,‡ Paul E. Irving,‡ M. J effrey Gobel,‡ and
Bryan W. Sherman‡
GlaxoSmithKline Research Laboratories, P.O. Box 13398, Research Triangle Park, North Carolina 27709-3398
Received December 20, 2000
A series of 2′-alkylthio-2-(anilinomethyl)imidazolines were prepared to examine the effect of
the alkyl group size, sulfur oxidation state, and phenyl ring substitution on ligand binding
and agonism of R-adrenergic receptor subtypes R1a, R1b, R1d, R2a, and R2c. Binding at all receptor
subtypes decreased for compounds in the sulfone oxidation state as compared to their sulfide
analogues. While sulfides were generally potent, nonselective agonists, sulfones exhibited R1a
subtype selectivity in a cell-based functional assay. Sulfone (32) was 250-7000-fold selective
for R1a vs all other subtypes.
In tr od u ction
Adrenergic receptor agonists selective for the R1
family have been used to prevent or reverse the hy-
potensive state associated with a variety of medical
conditions. They have also been used to treat nasal
congestion, mydriasis, and disorders of the lacrimal
gland.1 While compounds with selectivity for R1 vs R2
F igu r e 1.
adrenergic receptors have long been known, the more
recent cloning and expression of R1a, R1b, and R1d
receptor subtypes have allowed the search for com-
pounds with selectivity for individual subtypes within
the R1 family. Our interest in identifying selective R1a
agonists was derived from the limited success of R
adrenergic agonists phenylpropanolamine (41) (Figure
1), pseudoephedrine (42), and R-(aminomethyl)-2,5-di-
methoxybenzyl alcohol (43) (the active metabolite of
midodrine) in treating stress urinary incontinence and
the hypothesis that undesired cardiovascular effects
seen with these compounds might be diminished in
compounds with high functional selectivity for the R1a
receptor.2 Differential expression of R1 subtypes in
various tissues is well-documented,3 and while the role
of each R1 receptor subtype in urethral smooth muscle
tone and contraction is not fully understood, data
suggest that R1a selective agonists have an increased
likelihood of achieving an acceptable therapeutic index.4
N-[3-[(1R)-2-amino-1-hydroxyethyl]-4-fluorophenyl] meth-
anesulfonamide (44), an R1a selective agonist, has been
reported to provide selectivity for contraction of urethral
smooth muscle vs the cardiovascular effects in animals
and was recently evaluated in clinical trials for stress
urinary incontinence.5
F igu r e 2.
originally patented as pesticides,7 but 2-(anilinomethyl)
imidazolines are known to be adrenergic agonists.8
In an effort to identify structurally novel compounds
in this series, a medium throughput parallel synthesis
approach was developed. Commercially available anilines
were reacted with 2-chloromethylimidazoline hydro-
chloride in a Stemblock,9 and the crude products were
purified using a MultElute chromatography system to
give the desired products in a single step. From this set,
2′-methylthio-2-(anilinomethyl)imidazoline (1) was iden-
tified as a potent though nonselective R adrenergic
agonist (Table 1). Starting with this compound, varia-
tions of alkyl group size, sulfur oxidation state, and
phenyl ring substituents were examined in an effort
to identify R1a selective compounds.
Screening of our in-house compound collection using
cloned human R1a adrenoceptor in a cell-based func-
tional assay identified simple 2-(anilinomethyl)imida-
zolines as R1a adrenergic agonists.6 Some of these
compounds (for example, 45 and 46; Figure 2) were
Ch em istr y
Sulfoxide (2) and sulfones (3, 6, 10, 13, 17, 20, 23,
25, 28, 32, 36, and 40) were prepared via oxidation of
the corresponding sulfides (Scheme 1) typically using
meta-chloroperoxybenzoic acid as the oxidant.10 The
sulfides (1, 5, 9, 12, 16, 19, 22, 24, 27, 31, and 35) in
turn were prepared by alkylation of the corresponding
alkylthioanilines with 2-chloromethylimidazoline hy-
* To whom correspondence should be addressed. Stephen J . Hodson,
Proctor and Gamble Health Care Research Center, P.O. Box 8006,
Mason, OH 45040.
† Medicinal Chemistry Department.
‡ Receptor Biochemistry Department.
10.1021/jm000542r CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/26/2002

2230 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11
Ta ble 1. In Vitro Binding and Functional Dataa
Hodson et al.
R receptor binding (pki)
R1d R2a
7.95 7.32
functional agonism (pEC50) (% max)
no.
1
R
X
n
R1a
R1b
R2b
R2c
R1a
R1b
R1d
R2a
R2c
CH3
H
0
7.36
7.18
6.10
5.89
7.12
6.04
6.08
6.77
6.00
6.62
5.64
7.82
6.29
7.39
5.88
6.42
5.69
6.11
6.84
8.34
8.66
105
8.05
55
7.4
76
8.25
105
6.31
91
7.25
103
8.47
109
6.62
115
7.16
115
8.30
115
5.71
70
8.11
91
7.62
93
8.11
93
6.36
61
8.64
90
7.78
96
7.38
106
7.98
111
5.96
95
9.96
101
8.71
98
8.80
101
7.85
102
9.36
82
8.55
91
6.29
41
<4
82
2
CH3
CH3
Et
H
1
2
0
2
2
0
2
0
2
0
2
0
2
2
0
2
0
2
0
2
0
2
2
5.89
6.23
7.36
5.92
5.66
7.24
5.57
6.83
6.26
7.68
6.18
7.48
6.09
6.38
6.23
5.92
5.42
7.24
5.65
5.86
6.65
5.55
6.52
5.46
8.30
5.79
8.21
5.58
6.04
6.32
6.01
5.25
7.09
5.88
<5.2
<5.2
5.79
<5.3
<5.3
6.57
<4
<4
<5
<5
21
74
3
H
<4
<4
<5
11
6.60
67
<5
10
<5
23
6.38
5.5
68
7.55
101
5.3
64
5.5
56
7.55
91
<5
50
7.8
104
6.3
93
7.00
82
<5
32
8.25
97
5.7
91
6.35
93
8.1
5
H
7.86
82
<4
7.29
34
<4
6
Et
H
<5.2
<5.2
5.60
5.58
6.78
7
n-Pr
i-Pr
i-Pr
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
<5.1
<4
<4
9
H
7.09
5.53
6.78
5.63
7.21
29
<5
<5.3
<5.3
64
<5
14
10
12
13
16
17
19
20
23
24
25
27
28
31
32
35
36
37
40
H
<5.2
5.40
<5.3
3-F
3-F
4-F
4-F
5-F
5-F
6-F
6.66
6.59
6.66
7.07
48
<4
7.47
59
<4
7.00
102
<5
64
<5.1
<5.2
6.07
7.23
6.40
7.74
5.35
6.06
6.70
8.22
78
<4
8.04
75
<4
6.5
47
<5
19
<5.2
6.48
<5.3
6.94
8.73
92
<4
7.66
107
<4
7.60
96
<5
18
<5
38
<5
40
<5
33
<5.2
<5.2
<5.3
6.16
6.22
<4
<4
5-CF3
5-CF3
5-CH3
5-CH3
5-OCH3
5-OCH3
5-Cl
5.78
8.22
114
<4
7.36
58
<4
45
<5
25
<4.9
<5.0
<4.8
<5.1
<5.2
6.01
<5.3
6.70
7.68
6.11
6.76
5.79
7.73
6.27
6.34
6.21
6.91
5.46
6.16
5.34
7.16
5.53
6.19
5.67
7.76
5.32
6.97
5.12
8.33
5.62
6.06
7.20
5.41
6.66
5.44
7.38
9.38
96
6.85
91
8.44
92
<4
9.04
107
<5.7
7.60
8.05
81
5.95
76
6.70
74
5.48
49
8.55
92
6.10
81
<5
54
5.2
69
87
<5
24
<5.2
<5.2
<5.2
<5.3
6.22
8.30
91
<4
6.35
52
<5
16
<5.3
6.17
6.77
5.32
5.40
5.57
9.30
103
7.21
103
<4
8.57
106
<4
8.20
93
<5
42
<5
38
<5
29
5-Cl
<5.1
<5.2
<5.2
<5.2
4-Cl
5.30
6.10
<4
<4
<4.8
<4
44
5.95
7.80
4.95
6.08
6.80
109
7.69
74
<4.0
<4.6
<4.0
<4.6
<5.0
5.7
87
34
oxymetazoline
5.87
7.79
5.27
7.23
8.48
88
a
Each entry represents the mean of at least two experiments, with R1 pKi values having an average SEM of (0.08, R2 pKi values
having an average SEM of (0.13, R1 pEC50 values having an average SEM of (0.15, and R2 pEC50 values having an average SEM of
(0.10. “% max” refers to the maximum response observed for the compound expressed as a percentage of the maximum response observed
for a nonselective R1 (phenylephrine) or R2 (UK14 304) agonist and is indicative of the efficacy of the compounds relative to these full
agonists.
drochloride in the presence of phenol.7a An excess of the
aniline served as an acid scavenger, or in some cases,
2,6-lutidine was used as a base. Isolation of the product
imidazolines was accomplished by chromatography on
silica gel or alumina. Some compounds could be isolated
by partitioning the crude reaction mixture in water/CH2-
Cl2 and adjusting the pH to 7.0 with NaOH to allow
extraction of the excess aniline. Adjusting the pH to 12
allowed extraction of the free base into the organic
phase, and addition of HCl or fumaric acid precipitated
the product as its salt.
The aniline used for the preparation of 1 was com-
mercially available. Anilines 4, 8, 15, 18, 26, 30, and
34 were made by alkylation of the corresponding
thiophenols with the appropriate alkyl halide. The
aniline used for the preparation of 12 was obtained by
deprotection of its trifluoroacetamide derivative.11
The anilines used for the preparation of 16, 19, 27,
31, and 35 were made by hydrolysis of the appropriate
commercially available benzothiazole derivatives (Scheme
2) followed by alkylation with methyl iodide.12 The
aniline used for the preparation of 23 was prepared by

2-(Anilinomethyl)imidazolines as Receptor Agonists
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11 2231
Sch em e 1
Sch em e 3
Effect of Alk yl Gr ou p Size in Su lfid es. Lengthen-
ing the methyl group of 1 to give ethyl-substituted
compound (4) caused almost no change in affinity (pKi).
The largest effect, a 5-fold reduction, was seen at R1d.
Branching (as in isopropyl compound 9) also caused
little change in affinity at any receptor except at R1d,
where a 20-fold reduction was seen. Potency (pEC50) at
R1a, R1b, R2a, and R2c was also little affected by lengthen-
ing or branching (compounds 5 and 9). Changes of less
than 10-fold were observed. Lengthening (as in com-
pound 5) reduced potency at R1d by only 6-fold, but
branching (9) caused a nearly 1000-fold reduction in
potency. This parallels the observed affinity data in that
R1d suffers the largest affinity loss on alkyl group
enlargement and suggests that R1d has a significantly
different binding cavity than the other subtypes. This
cavity is unable to accommodate branching in the space
filled by the alkyl group of 9 resulting in 20-fold
decreased affinity. Moreover, the resulting complex fails
to induce the correct conformational change required
for receptor activation.
Effect of Su lfu r Oxid a tion Sta te. 2-(Anilinometh-
yl)imidazolines with amide or ketone substituents in the
2′-position exhibit interesting structure-activity rela-
tionships (SAR) with respect to R1 subtype selectivity.17
Hydrogen bonding between the 2′-amide or ketone
carbonyl and the aniline proton may affect the confor-
mation of these molecules in the receptor (Figure 3),
serving to restrict movement of the imidazoline and/or
the 2′-substituent. On the basis of the selectivity data,
it appears that the R1a receptor can generally accom-
modate this conformational restriction better than R1b
or R1d. We hypothesized that a sulfoxide or sulfone in
the 2′-position might also form a hydrogen bond and
lead to similar effects.
alkylation of 2,6-difluoronitrobenzene with sodium meth-
ylmercaptide followed by reduction of the nitro group.13
8-Aminothiochroman (39),14 used for the preparation of
40, was made by conversion of 8-nitrothiochroman-4-
one to the enol-triflate followed by hydrogenation of the
nitro group and hydrogenolysis of the enol triflate.
Compound 7 was prepared via alkylation of the o-
nitrophenylsulfinate, derived from the corresponding
sulfonyl chloride, with bromopropane (Scheme 3).15
Discu ssion
To model the potential ability of ligands to activate
the individual R adrenergic subtypes in humans, all
compounds were evaluated in a cell-based functional
assay using the cloned human receptors. Human R1a,
R1b, and R1d receptors were expressed in rat-1 fibro-
blasts, and agonist activity was evaluated via calcium
mobilization through the Gq-coupled PLC pathway
using calcium sensitive fluorescent dyes. Human R2a and
R2c receptors were expressed in Chinese hamster ovary
(CHO) cells, and agonist activity was evaluated via
cyclic adenosine 5′-monophosphate (cAMP) accumula-
tion (lack of a reliable high-throughput assay for the
human R2b receptor prevented us from evaluating all
compounds for R2b activity). The agonist potency (ex-
pressed as the pEC50) and efficacy (expressed as a
percent of the maximal effect of phenylephrine for R1
adrenoceptors or UK 14 304 for R2 adrenoreceptors) of
select analogues of 2′-methylthio-2-(anilinomethyl)imi-
dazoline are listed in Table 1. R1a, R1b, R1d, R2a, and R2c
receptor binding affinities for these compounds are also
listed in Table 1.16
We oxidized the methylthio group of 1, giving sulfone
3, to look for similar hydrogen-bonding effects. Methyl
sulfone 3 lost 15-fold affinity and 12-fold potency at R1a,
as compared to methyl sulfide 1, but still strongly
activated the receptor (pEC50 ) 7.25). While affinity at
Sch em e 2

2232 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11
Hodson et al.
F igu r e 5.
F igu r e 3.
F igu r e 6.
F igu r e 4.
receptor. The constrained analogue (40) is unable to
assume this conformation.
R1b decreased comparably (20-fold), potency at the R1b
receptor decreased remarkably, leaving 3 inactive at R1b.
This difference holds for the other subtypes as well.
Affinity for 3 at R1d, R2a, and R2c decreased between 9
and 340-fold, while potency decreased from 250- to
greater than 10 000-fold. The result is that sulfone 3 is
50- to greater than 10 000-fold selective for R1a vs R1b,
R1d, R2a, R2b, and R2c. Sulfide 1, while 12-fold more potent
at R1a, was only 1.5-9-fold selective for R1a vs the other
subtypes. While 3 did retain some activity at R2c, it was
a weak partial agonist (pEC50 ) 5.5, 68% maximum
potency of UK 14 304). Racemic sulfoxide 2 had half of
the affinity of sulfone 3 and was 9-fold less potent at
R1a. This suggests that both enantiomers of sulfoxide 2
are less potent agonists at R1a than sulfone 3. Compound
2 had similar affinity at R1b, R1d, and R2a. In 3, the
hydrogen bond formed by the sulfone induces a favor-
able receptor-bound conformation leading to R1a selec-
tivity. The hydrogen bond formed by sulfoxide 2 induces
a less favorable bound comformation, and selectivity for
R1a decreases. This hypothesis is further supported by
the observation that an analogue of 3 in which the
aniline NH was replaced by an oxygen (47; Figure 4)
was a very weak agonist at all receptors tested with
pEC50 ) 5.3 at R1b and less than 5.0 at the other
subtypes (unpublished data).
Effect of P h en yl Rin g Su bstitu tion . Compounds
1 and 3 were modified with a fluorine in most positions
on the aryl ring and with a variety of electron-donating
or -withdrawing substituents in the 5′-position. Our
focus on 2′,5′-substitution of the aniline ring was based
on the existence of a number of known R1a agonists with
similar substitution patterns, such as methoxamine
(48), 1,2,3,4-tetrahydro-8-methoxy-5-(methylthio)-2-
naphthaleneamine (49), and 2-(2-chloro-5-trifluoro-
methylphenylamino)-2-imidazoline (50) (Figure 5).18
Addition of a 5′-methyl group (27 and 28) resulted in
less than 5-fold changes in affinity as compared to the
unsubstituted compounds. Potency however was en-
hanced by 50-fold for the sulfide (R1a pEC50 ) 10.66)
and 30-fold for the sulfone. In contrast, addition of a
5′-trifluoromethyl group to the sulfide (24) resulted in
a 20-fold reduction in potency at R1a and a 250-fold
reduction in potency at R2a. The 5′-trifluoromethyl-
substituted sulfone 25 lost affinity and potency as
compared to 3, except at R2a. In general, electron-
withdrawing groups at the 5′-position of sulfoxide 3 had
a small negative impact on binding (up to 20-fold) that
was not subtype selective. The effect of the 5′-substitu-
ent on potency appears to depend both on size and on
electron-withdrawing/donating ability and is not always
selective for R1a vs the other subtypes. This further
suggests the role of hydrogen bonding in determining
the conformation of the bound molecule. Electron-
withdrawing substituents para to the sulfonyl group
would reduce the ability of the sulfone to participate in
hydrogen bond formation. The highest composite func-
tional selectivity for R1a vs all receptor subtypes was
seen for the 5′-methoxy-substituted sulfone (32). It is
notable that 32 was one of the weakest binding com-
pounds at R1a (pKi ) 5.79) but was still a potent full
agonist (R1a pEC50 ) 7.85, 102% maximum potency of
phenylephrine; Figure 6).
Effect of Alk yl Gr ou p Size on Su lfon es. Enlarging
the alkyl group in the sulfide series generally had little
effect on affinity or potency (except for branching at R1d),
and the trend was similar in the sulfone series. Com-
parison of sulfones 3, 6, 7, and 10 shows that linear or
branched alkyl group extension changed affinity by a
factor of 7 or less. Potency at R1a decreased by 8-fold
with a one carbon extension to 6, while n-propyl-
substituted 7 was nearly identical to 3 in potency.
Branching in compound 10 caused a 35-fold loss of
potency at R1a relative to methyl sulfone 3. Potency at
the other subtypes, already nearly absent in 3, remained
so with 6, 7, and 10. The weak partial agonism of 3 at
R2c was finally eliminated by branching in 10. Com-
pound 40, which can be thought of as a constrained
analogue of 7, had greater affinity at R1a than 7, nearly
equal to that of methyl sulfone 3, but lost all functional
activity except for weak agonism at R2c. These observa-
tions again suggest that a hydrogen bond involving the
sulfone group induces a bound conformation in 3, 6, 7,
and (to a lesser extent) 10, which activates the R1a
Con clu sion
The receptor affinity and functional data presented
point to the importance of hydrogen bonding in deter-
mining the conformation of the receptor-bound sulfones.
The complex formed by the sulfones with the R1a
receptor strongly activates the R1a receptor. The other
receptor subtypes interact with this conformation less
favorably, and the resulting complex fails to induce the

2-(Anilinomethyl)imidazolines as Receptor Agonists
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11 2233
forskolin-stimulated accumulation of cAMP in CHO cells
expressing human R2A or R2C adrenoceptors. For these assays,
cells were grown to 90% confluence in DMEM/F-12 supple-
mented with pyroxidine‚HCl, 15 mM HEPES, and 2 mM
L-glutamine, supplemented with heat-inactivated fetal bovine
serum (10%), G418 (500 µg/mL, GIBCO), L-glutamine (2 mM,
GIBCO), penicillin G (100 units/mL), and streptomycin sulfate
(100 µg/mL, GIBCO). The day prior to the assay, cells were
harvested using 0.05% trypsin, resuspended in culture media,
and plated in 96 well plates (100 µL, 40 000 cells/well). On
the day of the assay, the cells were washed in an assay buffer
comprised of DMEM/F-12 with pyroxidine‚HCl, HEPES (15
mM), L-glutamine (2 mM), and isobutylmethylxanthine (300
µM). Compounds or a nonselective R2 agonist, UK14 304 (RBI)
were added to the wells and incubated at 37 °C for 30 min.
Following this preincubation, forskolin (5 µM) was added to
the wells and the plates were incubated at 37 °C for an
additional 90 min. The assay was stopped by the removal of
media from the wells. cAMP levels were determined by assay
of the samples using standard Flashplate (DuPont/NEN)
techniques. Data were corrected for baseline accumulation and
expressed as percent inhibition of the response to forskolin
alone. Nonlinear regression of these normalized data was
performed to estimate the potency (pEC50) of the compounds.
conformational change required for strong activation.
The constrained sulfone (40) is unable to assume the
favorable conformation and loses potency at all recep-
tors. The sulfides, unconstrained by this hydrogen
bonding, are potent but generally nonselective agonists
at all R subtypes. From the existing data, it is not
possible to discern whether the hydrogen bond-induced
orientation of the 2′-subsitituent, the imidazoline ring,
or both are important in eliciting selective activation of
the receptor subtypes. Studies by Perez and co-workers
suggest that R adrenergic agonists containing a basic
nitrogen (such as an imidazoline) interact with the
receptor to interrupt an interhelical salt bridge.19 The
R1d receptor behaves quite differently than the other
subtypes toward the sulfides and tolerates almost no
steric volume in the 2-position. Several of the com-
pounds reported herein offer significant in vitro selec-
tivity advantages over 44. These selective R1a adreno-
ceptor agonists are useful tools to test the relationship
between R1a subtype selectivity and uroselectivity in
animal models. Progress toward a clinical candidate for
stress urinary incontinence from this series will be
reported in due course.
2′-Met h ylt h io-2-(a n ilin om et h yl)im id a zolin e H yd r o-
ch lor id e (1). 2-Methylmercaptoaniline (Aldrich Chemical Co.)
(166.6 g, 1.2 mol) and 2-chloromethylimidazoline hydrochloride
(75 g, 0.48 mol) were stirred at reflux in 2-propanol (375 mL)
for 21 h. The reaction mixture was allowed to cool, and the
solid was filtered. The solid was washed with ethyl acetate
and then stirred in 800 mL of 1:1 water:ethyl acetate. Sodium
hydroxide (1.0 N) (270 mL) was added to the heterogeneous
mixture, and the organic phase was discarded. To the aqueous
mixture was added 1 N NaOH (50 mL) followed by ethyl
acetate (300 mL). The layers were separated, and the pH of
the aqueous phase was adjusted to 10 with 1 N NaOH. The
basic aqueous phase was extracted with ethyl acetate (2 × 300
mL). The extracts were reduced to 100 mL under vacuum and
filtered. Ethyl acetate (1 L) was added to the filtrate, and
hydrogen chloride (4 N in 1,4-dioxane) (120 mL) was added
with stirring. A solid formed as the mixture was allowed to
cool to room temperature. The resulting product was collected
Exp er im en ta l Section
Deter m in a tion of Affin ity for r Ad r en ocep tor s. Affinity
of compounds at R1 adrenoceptor subtypes was determined by
radioligand binding techniques using membranes prepared
from Rat-1 fibroblasts expressing human R1a, R1b, or R1d
adrenoceptors as previously described.17 Affinity of compounds
at R2 adrenoceptor subtypes was determined by radioligand
binding techniques using membranes prepared from CHO cells
expressing human R2A, R2B, or R2C adrenoceptors as previously
described.17
Deter m in a tion of F u n ction a l Activity a t r1 Ad r en o-
cep tor s. Functional activity of compounds at R1 adrenoceptors
was assayed by determining their ability to induce an increase
in intracellular free calcium concentration in Rat-1 fibroblasts
expressing human R1A, R1B, or R1D adrenoceptors. Intracellular
free calcium concentrations were determined using the calcium
sensitive fluorescent dye Calcium Green (Molecular Probes)
and measured in a fluorescence imaging plate reader (FLIPR,
Molecular Devices). For these assays, cells were grown in 225
cm2 flasks in DMEM (GIBCO) supplemented with 10% heat-
inactivated fetal bovine serum (Hyclone), and 0.6 mg/mL G418
(Genetecin, GIBCO). Adhered cells were released with 1 mL
of trypsin solution (0.25%, Sigma), diluted in media, and added
to 96 well culture plates in a volume of 100 µL to give 6000
cells/well, and incubated for 48 h at 37 °C prior to loading and
assay.
On the day of assay, cells were washed once with assay
buffer (145 mM NaCl, 5 mM KCl, 0.5 mM CaCl2, 1 mM MgCl2,
10 mM HEPES, and 10 mM glucose, pH 7.4). The washed cells
were then loaded with Calcium Green by incubating for 2 h
at 37 °C in assay buffer containing Calcium Green (4 µM),
pluronic acid (0.2%), and probenecid (2.5 mM). After they were
loaded, the plates were washed twice with assay buffers and
allowed to come to room temperature. Plates were then
transferred to the FLIPR, and baseline fluorescence was
recorded for 10 s, followed by addition of compounds and
continuous monitoring of fluorescence for 50 s. The maximum
response observed in the presence of compound was corrected
for the baseline measurement and expressed as a percent of
the corrected response to a maximal concentration of the
nonselective R1 agonist phenylephrine. Nonlinear regression
of these normalized data was performed to estimate the
potency (pEC50) of the compounds.
1
to give 1 (97 g, 73%). H NMR (400 MHz; DMSO-d6): δ 10.0
(br s, 2H), 7.3 (d, J ) 8.0 Hz, 1H), 7.2 (dd, J ) 8.0 Hz, 1H), 6.7
(dd, J ) 8.5 Hz, 1H), 6.45 (d, J ) 8.5 Hz, 1H), 5.95 (t, J ) 5.5
Hz, 1H), 4.3 (d, J ) 5.5 Hz, 2H), 3.8 (s, 4H), 2.35 (s, 3H). MS
(ESI): 222 (M + H). Anal: CHNSCl.
2′-Met h ylsu lfin yl-2-(a n ilin om et h yl)im id a zolin e H y-
d r och lor id e (2). Compound 1 (2.3 g, 8.9 mmol) was dissolved
in water (20 mL) and cooled to 0 °C. A solution of OXONE
(3.4 g, 5.5 mmol) in 30 mL of water was added dropwise (28
mL used) until conversion of starting material was complete
as seen by HPLC (Luna C18 3 µm × 50 mm × 2 mm; 1 mL/
min 0-95% CH3CN:H2O/8 min; 220 nm detection). Ethyl
acetate was added (50 mL), and the pH was adjusted to 12
with 5 N KOH. The organic phase was separated, filtered
through Celite, and evaporated in vacuo. The resulting resin
was dissolved in 2-propanol (10 mL) and treated dropwise with
a solution of concentrated HCl (0.6 mL) in 2-propanol (5 mL)
until precipitation was complete. The resulting white powder
was recrystallized twice from hot 2-propanol to give 2 (1.1 g,
44%) as a white powder. 1H NMR (400 MHz; DMSO-d6): δ
10.2 (br s, 2H), 7.47 (d, J ) 6.9 Hz, 1H), 7.32 (dd, J ) 8.0 Hz,
1H), 6.87 (dd, J ) 7.5 Hz, 1H), 6.6 (d, J ) 8.2 Hz, 1H), 6.5 (t,
J ) 5.8 Hz, 1H), 4.3 (m, 2H), 3.8 (s, 4H), 2.8 (s, 3H). MS (ESI):
238 (M + H). Anal: CHNSCl.
2′-Met h ylsu lfon yl-2-(a n ilin om et h yl)im id a zolin e H y-
d r och lor id e (3). Compound 1 (5.0 g, 19.4 mmol) was dissolved
in water (18 mL) and cooled to -8 °C in an ice bath. The
resulting stirred slurry was treated with a solution of OXONE
(15.8 g, 25.7 mmol) in water (55 mL) in a slow stream while
the temperature was maintained below 10 °C. The mixture
was allowed to warm to room temperature and stirred for 30
min. 1-Butanol (50 mL) was added to the reaction mixture
Deter m in a tion of F u n ction a l Activity a t r2 Ad r en o-
cep tor s. Functional activity of compounds at R2 adrenoceptor
subtypes was assayed by determining their ability to inhibit

2234 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11
Hodson et al.
followed by 20 mL of 5 N KOH. The layers were separated,
and the aqueous layer was extracted with 1-butanol (50 mL).
The 1-butanol extracts were combined and treated with 1 N
HCl until the pH was ∼2.0. The mixture was heated to reflux
to reduce the volume until crystals appeared. The mixture was
allowed to cool and stir for 1 h, and the resulting crystals were
collected and dried in vacuo at 50 °C to give 3, (4.0 g, 71%).
1H NMR (400 MHz; DMSO-d6): δ 10.3 (br s, 1H), 7.65 (d, J )
8.0 Hz, 1H), 7.50 (dd, J ) 7.8 Hz, 1H), 6.9 (ddd, J ) 7.5 Hz,
2.7 Hz, 1H), 6. 7 (m, 2H), 4.42 (d, J ) 5.7 Hz, 2H), 3.8 (s, 4H),
3.2 (s, 3H). MS (ESI): 254 (M + H). Anal: CHNSCl.
2-Eth ylth ioa n ilin e (4).23 2-Aminothiophenol (Lancaster
Chemical Company) (5.0 g, 40 mmol) was stirred in dry ethanol
(100 mL) and cooled in an ice bath. Potassium t-butoxide (4.5
g, 40 mmol) was added portionwise to the solution over 15 min,
and the mixture was stirred for an additional 45 min. Ethyl
iodide (3.3 mL, 41 mmol) was added dropwise to the reaction
mixture over 15 min. The mixture was allowed to warm to
room temperature and then stirred for 45 min. The reaction
mixture was filtered, and the filtrate was evaporated to
dryness in vacuo. The resulting residue was treated with
methylene chloride (100 mL) and filtered, and the filtrate was
evaporated to dryness under vacuum to give 4 (5.2 g, 85%).
1H NMR (300 MHz; DMSO-d6): δ 7.2 (dd, J ) 7.7 Hz, 1.2 Hz,
1H), 7.0 (ddd, J ) 7.7 Hz, 1.4 Hz, 1H), 6.7 (dd, J ) 7.7 Hz, 1.0
Hz, 1H), 6.5 (ddd, J ) 7.4 Hz, 1.1 Hz, 1H), 5.2 (br s, 2H), 2.7
(q, J ) 7.3 Hz, 2H), 1.1 (t, J ) 7.3 Hz, 3H). The product was
used in the subsequent reaction without further analysis or
purification.
2′-E t h ylt h io-2-(a n ilin om et h yl)im id a zolin e F u m a r a t e
(5). Compound 4 (1.0 g, 6.53 mmol), 2-chloromethylimidazoline
hydrochloride (0.9 g, 5.8 mmol), 2,6-lutidine (0.7 mL, 5.8
mmol), and phenol (0.6 g) were mixed and heated in a 120 °C
oil bath under nitrogen for 30 min. The mixture was stirred
with water (10 mL) and washed twice with methylene chloride
(5 mL). Sodium hydroxide (1.0 N) (2.9 mL) was added to the
reaction mixture, and the solution was washed with methylene
chloride (2 × 5 mL). The layers were separated, and the
aqueous phase was evaporated in vacuo to give 0.54 g of the
crude product. A second reaction was run similarly to give 0.69
g of the crude product. The crude products obtained from these
reactions were combined and treated with methylene chloride
(60 mL), water (20 mL), and 1.0 N NaOH (5 mL). The organic
phase was dried (MgSO4) and filtered. The filtrate was added
rapidly to a stirred solution of fumaric acid (0.52 g, 4.5 mmol)
in methanol (10 mL), and the mixture was allowed to stand
for 1 h. The resulting crystals were collected and dried under
vacuum to provide 5 (0.73 g, 29%). 1H NMR (300 MHz; DMSO-
d6): δ 10.0 (br s, 2H), 7.35 (dd, J AB ) 7.3 Hz, J AC ) 1.2 Hz,
1H), 7.15 (dd, J ) 7.7 Hz, 1H), 6.63 (dd, J ) 7.8 Hz, 1H), 6.55
(d, J ) 7.8 Hz,1H), 6.45 (s, 2H), 6.1 (t, J ) 6.1 Hz, 1H), 4.2 (d,
J ) 6.1 Hz, 2H), 3.7 (s, 4H), 2.75 (q, J ) 7.3 Hz, 2H), 1.1 (t, J
) 7.4 Hz, 3H). MS (ESI): 236 (M + H). Anal: CHNS.
zenesulfonyl chloride (47 g, 212 mmol) was added to the
aqueous mixture in several portions over 90 min, and the
mixture was stirred for 2 h at 80 °C. The reaction mixture
was allowed to cool to ambient temperature. The resulting
solid was collected, washed with ice water, and dried in vacuo
to give the intermediate sulfinic acid (crude yield 28.6 g). The
crude sulfinic acid (9.5 g) was treated with sodium bicarbonate
(11 g), water (5 mL), and 1-bromopropane (9.8 mL). The
mixture was stirred, and an additional 15 mL of water was
added over 1 h. The mixture was heated to 90 °C under
nitrogen and stirred for 16 h. After it was cooled, the mixture
was extracted with toluene (3 × 100 mL) and the combined
extracts were concentrated in vacuo to give crude 2-propyl-
sulfonyl nitrobenzene (0.6 g). Silica gel chromatography (7:1
hexane:CH2Cl2) gave pure product (0.34 g). Reduction with
hydrogen (50 psi) and 5% Pd on carbon (0.1 g) in ethanol (50
mL) for 1 h gave 2-propylsulfonyl aniline (0.29 g, 1.45 mol).
This solid was mixed with 2-chloromethylimidazoline-hy-
drochloride (0.45 g, 2.9 mmol) in 2-propanol (2 mL) and
immersed in a 130 °C oil bath under a stream of nitrogen.
Additional 2-propanol was added twice over 2 h to remix the
resulting resin. The reaction mixture was dissolved in metha-
nol and adsorbed onto basic alumina. The crude product was
purified on basic alumina using CH2Cl2:MeOH (9:1). Fractions
containing the desired product were combined and concen-
trated to 5 mL. Treatment with 4 N HCl in dioxane (1 mL)
1
gave 7 (17 mg). H NMR (300 MHz; CD3OD): δ 7.75 (d, J )
7.8 Hz, 1H), 7.55 (dd, J ) 6.6 Hz, 1H), 6.95 (dd, J ) 7.3 Hz,-
1H), 6.8 (d, J ) 7.1 Hz, 1H), 4.45 (br s, 2H), 4.4 (s, 4H), 3.2 (t,
J ) 7.5 Hz, 2H), 1.7 (tq, J ) 7.3 Hz, 2H), 1.0 (t, J ) 7.3 Hz,
3H). MS (ESI): 282 (M + H). Anal: CHNSCl.
2-Isop r op ylth ioa n ilin e (8).24 2-Aminothiophenol (Lan-
caster Chemical Company) (2.34 g, 18.7 mmol) was stirred in
dry ethanol (50 mL) and cooled in an ice bath. Potassium
t-butoxide (2.1 g, 18.7 mmol) was added portionwise over 5
min, and the mixture was stirred for an additional 5 min.
Isopropyl iodide (1.9 mL, 19 mmol) was added dropwise to the
reaction mixture. After 1 h, the mixture was diluted with 50
mL of CH2Cl2 and filtered to remove KI. The filtrate was
concentrated in vacuo to give 8 (2.02 g, 59%). 1H NMR (300
MHz; DMSO-d6): δ 7.2 (d, J ) 7.7 Hz, 1H), 7.05 (dd, J ) 7.7
Hz, 1H), 6.7 (d, J ) 7.7 Hz, 1H),), 6.5 (dd, J ) 7.7 Hz, 1H), 5.3
(br s, 2H), 2.7 (dq, J ) 6.8 Hz, 1H), 1.15 (t, J ) 6.8 Hz, 6H).
The product was used in the subsequent reaction without
further analysis or purification.
2′-Isop r op ylth io-2-(a n ilin om eth yl)im id a zolin e Hyd r o-
ch lor id e (9). Compound 8 (0.4 g, 2.4 mmol), 2-chlorometh-
ylimidazoline hydrochloride (0.33 g, 2.15 mmol), 2,6-lutidine
(0.28 mL, 2.4 mmol), and 2-propanol (1 mL) were mixed and
immersed in a 120 °C oil bath under nitrogen for 5 h. The
resulting resin was allowed to cool and then stirred with
methylene chloride (10 mL). The suspension was filtered to
give an off-white solid, which was dissolved in methanol (2
mL) and treated with 4.0 N HCl in dioxane (125 µL) and
concentrated under vacuum to give 7, (212 mg, 31%). 1H NMR
(300 MHz; DMSO-d6): δ 10.2 (br s, 2H), 7.35 (dd, J ) 7.5 Hz,
1.2 Hz, 1H), 7.2 (dd, J ) 7.0 Hz, 1H), 6.65 (dd, J ) 7.3 Hz,
1H), 6.55 (d, J ) 8.1 Hz, 1H), 6.2 (br s, 2H), 4.4 (br s, 2H), 3.6
(s, 4H), 3.2 (dq, J ) 6.8 Hz, 1H), 1.2 (d, J ) 6.6 Hz, 6H). MS
(ESI): 250 (M + H). Anal: CHNSCl.
2′-Isop r op ylsu lfon yl-2-(a n ilin om eth yl)im id a zolin e F u -
m a r a te (10). Compound 9 (0.2 g, 0.7 mmol) was stirred in
methylene chloride (10 mL) and treated with meta-chloroper-
oxybenzoic acid (0.21 g, of 70 wt %) and methanol (1 mL). After
1 h, the solvent was evaporated and the crude product was
chromatographed on basic alumina (1-20% methanol/meth-
ylene chloride). The desired fractions were combined and
concentrated to give 0.13 g of the free base. The amine was
dissolved in methylene chloride (6 mL) and treated with
fumaric acid (0.055 g) in methanol (1.5 mL). The resulting
crystals were collected and dried under vacuum to give 10 (0.14
g, 54%). 1H NMR (300 MHz; DMSO-d6): δ 7.5 (m, 2H), 6.75
(m, 3H), 6.5 (s, 2H), 5.8 (br s, 2H), 4.3 (br s, 2H), 3.6 (s, 4H),
2′-Eth ylsu lfon yl-2-(a n ilin om eth yl)im id a zolin e F u m a -
r a te (6). Compound 5 (0.42 g, 1.2 mmol) was dissolved in
methylene chloride (20 mL) and methanol (6 mL) and treated
with 3-chloroperoxybenzoic acid (0.5 g of 85 wt %). After 1 h,
the mixture was concentrated and diluted with methylene
chloride (20 mL), water (3 mL), and 10 N sodium hydroxide
(1 mL). The mixture was agitated, and the methylene chloride
layer was separated. The organic solution was dried (MgSO4)
and filtered, and the filtrate was poured into a solution of
fumaric acid (0.15 g, 0.13 mmol) in methanol (4 mL). The
resulting crystals were collected and dried under vacuum to
1
give 6 (0.28 g, 60%). H NMR (400 MHz; DMSO-d6): δ 10.95
(br s), 7.60 (d, J ) 7.5 Hz, 1H), 7.50 (dd, J ) 7.5 Hz, 1H), 6.85
(dd, J ) 7.5 Hz, 1H), 6.78 (d, J ) 7.5 Hz, 1H), 6.73 (t, J ) 5.8
Hz, 1H), 6.46 (s, 2H), 4.23 (d, J ) 5.8 Hz, 2H), 3.70 (s, 4H),
3.28 (q, J ) 7.5 Hz, 2H), 1.08 (t, J ) 7.5 Hz, 3H). MS (ESI):
268 (M + H). Anal: CHNS.
2′-P r op ylsu lfon yl-2-(a n ilin om et h yl)im id a zolin e H y-
d r och lor id e (7). Sodium hydrogensulfite (50 g, 480 mmol),
sodium bicarbonate (35 g, 416 mmol), and water (200 mL) were
combined, and the mixture was heated to 80 °C. 2-Nitroben-

2-(Anilinomethyl)imidazolines as Receptor Agonists
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11 2235
3.4 (dq, J AB ) 6.8 Hz, 1H), 1.2 (d, J ) 6.8 Hz, 6H). MS (ESI):
282 (M + H). Anal: CHNS.
(residual acetic acid). The product was used in the subsequent
reaction without further purification or analysis.
2-Meth ylth io-4-flu or oa n ilin e (15). Compound 14 (5.5 g,
30 mmol) was stirred in ethanol (250 mL) and treated with
potassium t-butoxide (3.9 g, 35 mol) portionwise over 10 min.
Methyl iodide (1.9 mL, 30 mmol) was added dropwise, and the
reaction was stirred for 2 h. The mixture was filtered, and the
filtrate was concentrated in vacuo. The residue was triturated
with CH2Cl2 (200 mL), and the solid was filtered. The crude
product was chromatographed on silica gel (CH2Cl2/MeOH, 9:1)
to give 15 (2.25 g, 43%). 1H NMR (300 MHz; DMSO-d6): δ
6.95 (dd, J AB ) 9.5 Hz, J AC ) 2.9 Hz 1H), 6.77 (ddd, J ) 8.8
Hz, 3.0 Hz, 1H), 6.66 (d, J ) 5.3 Hz, 1H), 6.63 (d, J ) 5.3 Hz
1H), 4.95 (br s, 2H), 2.35 (s, 3H). The product was used in the
subsequent reaction without further purification or analysis.
3-F lu or o-2-(m eth ylth io)a n ilin e (11). N-(2-Methylthio-3-
fluorophenyl)trifluoroacetamide11 (2.36 g crude, 9.33 mmol)
was taken up in methanol (40 mL), and solid potassium
hydroxide (1.57 g, 28.0 mmol) was added portionwise at room
temperature. The mixture was heated to reflux. After 1.5 h,
the mixture was cooled to room temperature, and the solvent
volume was reduced to 5 mL by evaporation under reduced
pressure. The residue was taken up in deionized water (30
mL) and extracted with diethyl ether (3 × 40 mL). The extracts
were combined, washed with saturated sodium chloride solu-
tion, dried over sodium sulfate, and filtered, and the filtrate
was concentrated by evaporation under reduced pressure. The
crude product was purified by silica gel chromatography using
10% ethyl acetate in hexanes to give 1.2 g of 11. 1H NMR (400
MHz; DMSO-d6): δ 7.04 (dd, J ) 14.9 Hz, 8.1 Hz, 1H), 6.55
(d, J ) 8.2 Hz, 1H) 6.36 (dd, J ) 8.2 Hz, 8.2 Hz, 1H), 5.71 (s,
2H), 2.22 (s, 3H). The product was used in the subsequent
reaction without further analysis or purification.
2′-Met h ylt h io-4′-flu or o-2-(a n ilin om et h yl)im id a zolin e
F u m a r a te (16). Compound 15 (2.25 g, 13.31 mmol) was mixed
with 2-chloromethylimidazoline hydrochloride (1.86 g, 12
mmol), 2,6-lutidine (1.63 mL, 14 mmol), and phenol (1.5 g).
The reaction mixture was immersed in a 120 °C oil bath under
nitrogen for 20 min. The mixture was diluted with methylene
chloride (20 mL) and water (20 mL). The layers were sepa-
rated, and the aqueous phase was washed with methylene
chloride (2 × 10 mL). Sodium hydroxide (10 N) (2 mL) was
added to the aqueous phase, and the mixture was extracted
with methylene chloride (3 × 10 mL). The combined extracts
were dried (MgSO4) and filtered, and the filtrate was concen-
trated in vacuo to give 2.29 g of the crude product. The crude
product was dissolved in methylene chloride (100 mL) and
added to a solution of fumaric acid (1.04 g) in methanol (25
mL) and stored at 4 °C overnight. The resulting product was
2′-Met h ylt h io-3′-flu or o-2-(a n ilin om et h yl)im id a zolin e
F u m a r a te (12). Compound 11 (1.03 g, 6.56 mmol), 2-chlo-
romethylimidazoline hydrochloride (0.508 g, 3.28 mmol), and
phenol (0.75 g) were heated at 145 °C for 1.5 h under a nitrogen
atmosphere. After it was cooled, the residue was taken up in
deionized water (100 mL) and diethyl ether (75 mL). The
aqueous layer was separated, and the pH was adjusted to
approximately 8 with 1 N sodium hydroxide. The aqueous
mixture was washed with diethyl ether, and the pH was
adjusted to 12 with 10 N sodium hydroxide. The product was
extracted with diethyl ether (2 × 50 mL) and ethyl acetate (2
× 50 mL). The organic extracts were combined, dried over
sodium sulfate, and filtered, and the filtrate was concentrated
under reduced pressure. The free base (0.40 g) was dissolved
in ethyl acetate and treated with fumaric acid (0.194 g) in
methanol to produce a precipitate. Filtration gave 12 (0.49 g,
42%). 1H NMR (400 MHz; DMSO-d6): δ 7.22 (dd, J ) 15.3
Hz, 7.8 Hz, 1H), 6.55 (dd, J ) 8.6 Hz, 1H), 6.37-6.50 (m, 4H),
4.21 (d, J ) 5.8 Hz, 2H), 3.72 (s, 4H), 2.26 (s, 3H). MS (ESI):
240 (M + H). Anal: CHNS.
2′-Meth ylsu lfon yl-3′-flu or o-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (13). Compound 12 (0.465 g, 1.31 mmol) was
dissolved in methanol (20 mL) and dichloromethane (10 mL)
under a nitrogen atmosphere, and m-chloroperoxybenzoic acid
(0.75 g of 57-86% pure material) was added portionwise. The
mixture was stirred at room temperature for 16 h. The
volatiles were removed by evaporation under reduced pressure.
The residue was slurried in deionized water (40 mL) and
washed with ethyl acetate (2 × 30 mL). The aqueous layer
was adjusted to pH 12 using 3 N sodium hydroxide. The
product was extracted with ethyl acetate (2 × 60 mL), dried
over magnesium sulfate, and filtered, and the filtrate was
concentrated under reduced pressure to give 0.118 g of the
free base. The sulfone was taken up in ethyl acetate and
treated with fumaric acid (0.050 g) in methanol to produce a
precipitate. Filtration gave 13 (0.121 g, 24%). 1H NMR (400
MHz; DMSO-d6): δ 7.67 (t, J ) 5.6 Hz, 1H); 7.47 (dd, J )
15.1 Hz, 8.4 Hz, 1H); 6.63 (dd, J ) 11.3 Hz, 8.1 Hz, 1H), 6.46-
6.65 (m, 3H); 4.26 (d, J ) 5.6 Hz, 2H); 3.69 (s, 4H); 3.36 (s,
3H). MS (ESI): 272 (M + H). Anal: CHNS.
1
filtered and dried under vacuum to give 16 (2.12 g, 65%). H
NMR (300 MHz; DMSO-d6): δ 7.1 (dd, J ) 9.1 Hz, 2.9 Hz 1H),
6.91 (ddd, J ) 8.8 Hz, 3.0 Hz, 1H), 6.5 (d, J ) 5.3 Hz, 1H),
6.46 (d, J ) 5.3 Hz 1H), 6.42 (s, 2H), 5.7 (t, J ) 5.9 Hz, 1H),
4.15 (d, J ) 5.8 Hz, 2H), 2.40 (s, 3H). MS (ESI): 240 (M + H).
Anal: CHNS.
2′-Meth ylsu lfon yl-4′-flu or o-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (17). Compound 16 (1.9 g, 5.35 mmol) was
stirred in methanol (30 mL) and methylene chloride (100 mL)
and treated with 3-chloroperoxybenzoic acid (3.25 g of 85 wt
%). After 1 h, the mixture was concentrated in vacuo. To the
crude product was added methylene chloride (70 mL), water
(20 mL), and 10 N sodium hydroxide (2 mL). The organic phase
was separated, dried (MgSO4), and filtered, and the filtrate
was concentrated under vacuum to give 1.16 g of the free. The
free base was dissolved in methylene chloride (60 mL) and
added to a solution of fumaric acid (0.495 g) in methanol (12
mL). The resulting crystals were collected and dried in vacuo
to give 17 (0.95 g, 46%). 1H NMR (400 MHz; DMSO-d6): δ 7.4
(d, J ) 8.1 Hz, 2H), 6.8 (m, 1H), 6.58 (t, J ) 5.6 Hz, 1H), 6.45
(s, 2H), 4.3 (d, J ) 5.6 Hz, 2H), 3.7 (s, 4H), 3.3 (s, 3H). MS
(ESI): 272 (M + H). Anal: CHNS.
5-F lu or o-2-(m eth ylth io)a n ilin e (18). 5-Fluoro-2-methyl-
benzothiazole (10.03 g, 60 mmol) was slurried in a mixture of
ethylene glycol (45 mL) and 10 N sodium hydroxide (45 mL)
and heated to reflux under a nitrogen atmosphere. After 2 h,
the solution was cooled to 0 °C and treated with concentrated
hydrochloric acid to pH 7. The product was extracted with
ethyl acetate (3 × 75 mL), dried over magnesium sulfate, and
filtered, and the filtrate was concentrated under reduced
pressure to yield 3.28 g of crude 2-amino-4-fluorothiophenol.
The crude 2-amino-4-fluorothiophenol was dissolved in abso-
lute ethanol (50 mL) and cooled to 0 °C under a nitrogen
atmosphere. Potassium tert-butoxide (2.83 g, 25.23 mmol) was
added portionwise to the thiophenol solution, and the reaction
mixture was stirred for 15 min. Iodomethane (3.34 g, 23.5
mmol) in tetrahydrofuran (15 mL) was added dropwise to the
cold solution, and a thick precipitate formed. After the addition
was complete, the slurry was stirred for 30 min. The volatiles
were removed by evaporation under reduced pressure. The
residue was taken up in deionized water (30 mL) and 10 N
sodium hydroxide. (5 mL). The mixture was extracted with
diethyl ether (3 × 50 mL). The extracts were combined, washed
2-Mer ca p to-4-flu or oa n ilin e (14). 2-Amino-6-fluoroben-
zothiazole (5.0 g, 29.7 mmol) (Aldrich Chemical Co.) was
stirred in 120 mL of 10 N NaOH in a 500 mL three-necked
round-bottomed flask, which was fitted with a reflux con-
denser. The reaction mixture was heated at 120 °C under a
slow stream of nitrogen. After 2 h, the nitrogen stream was
no longer basic to wet litmus paper. The reaction mixture was
allowed to cool, treated with 1 g of decolorizing carbon, and
filtered. The filtrate was treated with acetic acid (70 mL) to
adjust the pH to 5.0. The resulting precipitate was collected,
washed with water, and dried under vacuum to give 14 (5.5
1
g, 130%). H NMR (300 MHz; DMSO-d6): δ 6.9 (d, J ) 9 Hz,
1H), 6.6 (m, 3H), 6.1 (br s, 2H), 3.35 (br s, 1H), 1.9 (s, 2H)

2236 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11
Hodson et al.
with saturated sodium chloride solution, dried over magnesium
sulfate, and filtered, and the filtrate was concentrated under
reduced pressure. The product was purified by silica gel
chromatography using 5% ethyl acetate in hexanes to give 1.37
g of 18. 1H NMR (400 MHz; DMSO-d6): δ 7.21 (dd, J ) 8.6
Hz, 6.9 Hz, 1H); 6.46 (dd, J ) 11.5 Hz, 2.8 Hz, 1H); 7.21 (ddd,
J ) 8.6 Hz, 2.8 Hz, 1H); 5.55 (s, 2H); 2.22 (s, 3H). The product
was used in the subsequent reaction without further analysis
or purification.
(3 × 5 mL). The extracts were combined, dried (MgSO4), and
filtered, and the filtrate was concentrated to 40 mL. The free
base was treated with a solution of fumaric acid (0.4 g, 3.5
mmol) in methanol (10 mL). The resulting precipitate was
1
collected to give 22 (0.15 g, 0.42 mmol). H NMR (300 MHz;
DMSO-d6): δ 7.2 (d, J ) 8.1 Hz, 1H), 7.05 (dd, J ) 7.8 Hz, 5.1
Hz, 1H), 6.7 (m, 1H), 5.5 (br s, 1H), 4.2 (s, 2H), 3.8 (s, 4H), 2.4
(s, 3H). The product was used in the subsequent reaction
without further analysis or purification.
2′-Met h ylt h io-5′-flu or o-2-(a n ilin om et h yl)im id a zolin e
F u m a r a te (19). Compound 18 (1.01 g, 6.44 mmol), 2-chlo-
romethylimidazoline hydrochloride (0.499 g, 3.22 mmol), and
phenol (0.80 g) were heated at 145 °C for 1.5 h under a nitrogen
atmosphere. After it was cooled, the residue was taken up in
deionized water (100 mL) and diethyl ether (75 mL). The
aqueous layer was separated and treated with 1 N sodium
hydroxide to adjust the pH to 8. The aqueous layer was washed
with ethyl acetate, and the layers were separated. The pH of
the aqueous phase was adjusted to 12 with 10 N sodium
hydroxide. The product was extracted with ethyl acetate (3 ×
50 mL). The extracts were combined, dried over magnesium
sulfate, and filtered, and the filtrate was concentrated under
reduced pressure to give 0.53 g of the desired free base. The
free base was dissolved in ethyl acetate and treated with a
solution of fumaric acid (0.256 g) in methanol to produce a
precipitate. Filtration gave 19 (0.66 g, 22%). 1H NMR (400
MHz; DMSO-d6): δ 7.37 (dd, J ) 6.8 Hz, 8.2 Hz, 1H), 6.43-
6.50 (m, 3H), 6.41 (dd, J ) 12.0 Hz, 2.6 Hz, 1H), 6.29 (t, J )
6.0 Hz, 1H), 4.19 (d, J ) 6.0 Hz, 2H), 3.72 (s, 4H), 2.29 (s,
3H). MS (ESI): 240 (M + H). Anal: CHNS.
2′-Meth ylsu lfon yl-6′-flu or o-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (23). Compound 22 (0.15 g, 0.42 mmol) was
dissolved in methanol (5 mL) and treated with meta-chloro-
peroxybenzoic acid (100 mg, 70 wt %). After 30 min, the
mixture was concentrated under vacuum and diluted with
methylene chloride (6 mL) and 1 N sodium hydroxide (2 mL).
The organic phase was separated, dried (Na2SO4), and filtered,
and the filtrate was added to a solution of fumaric acid (45
mg, 0.38 mmol) in methanol (1 mL). The resulting solid was
collected and dried under vacuum to give 23 (0.145 g, 88%).
1H NMR (400 MHz; CD3OD): δ 7.65 (d, J ) 8.0 Hz, 1H), 7.4
(dd, J ) 8.1 Hz, 5.6 Hz, 1H), 7.0 (ddd, J ) 8.1 Hz, 4.5 Hz, 1H),
6.65 (s, 2H), 4.5 (d, J ) 4.8 Hz, 2H), 4.0 (s, 4H), 3.2 (s, 3H).
MS (ESI): 272 (M + H). Anal: CHNS.
2′-Meth ylth io-5′-tr iflu or om eth yl-2-(a n ilin om eth yl)im i-
d a zolin e F u m a r a t e (24). 3-Amino-4-(methylthio)benzotri-
fluoride (1.0 g, 4.83 mmol., Lancaster Chemical Company),
2-chloromethylimidazoline hydrochloride (0.372 g, 2.4 mmol),
and phenol (0.3 g) were heated under a nitrogen atmosphere
at 140 °C for 2 h. After it was cooled, the residue was taken
up in deionized water (75 mL) and diethyl ether (75 mL). The
aqueous layer was separated and treated with 1 N sodium
hydroxide to pH 7. The solution was washed with diethyl ether
(75 mL). The aqueous layer was separated and treated with 1
N sodium hydroxide to pH 12. The product was extracted with
ethyl acetate (3 × 25 mL). The extracts were combined, dried
over sodium sulfate, and filtered, and the filtrate was concen-
trated under reduced pressure. The residue was taken up in
ethyl acetate and treated with fumaric acid (1 equiv) in
methanol to produce a precipitate. Filtration gave 24 (0.69 g,
2′-(Meth ylsu lfon yl-5′-flu or o-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (20). Compound 19 (0.465 g, 1.31 mmol) was
dissolved in methanol (20 mL) and dichloromethane (10 mL)
under a nitrogen atmosphere, and m-chloroperoxybenzoic acid
(0.532 g of 57-86% pure material) was added portionwise. The
mixture was stirred at room temperature for 1.5 h. The
volatiles were removed by evaporation under reduced pressure.
The residue was slurried in deionized water (40 mL) and
washed with ethyl acetate (2 × 30 mL). The pH of the aqueous
layer was adjusted to 12 with 3 N sodium hydroxide. The
product was extracted with ethyl acetate (2 × 60 mL), dried
over magnesium sulfate, and filtered, and the filtrate was
concentrated under reduced pressure to give 0.340 g of the
desired sulfone. The free base was taken up in ethyl acetate
and treated with fumaric acid (0.145 g) in methanol to produce
1
71%). H NMR (400 MHz; DMSO-d6): δ 7.44 (d, J ) 8.0 Hz,
1H), 7.01 (d, J ) 8.0 Hz, 1H); 6.77 (s, 1H); 6.48 (s, 2H), 6.06
(br s, 1H), 4.20 (d, J ) 5.4 Hz, 2H), 3.69 (s, 4H), 2.47 (s, 3H).
MS (ESI): 290 (M + H). Anal: CHNS.
2′-Meth ylsu lfon yl-5′-tr iflu or om eth yl-2-(an ilin om eth yl)-
im id a zolin e F u m a r a te (25). Compound 24 (0.614 g, 1.5
mmol) was dissolved in methanol (10 mL) under a nitrogen
atmosphere. m-Chloroperoxybenzoic acid (0.610 g of 57-86%
pure material) was added portionwise. The mixture was stirred
at room temperature for 1.5 h. The mixture was poured into
deionized water (35 mL) and diethyl ether (45 mL). The
aqueous layer was separated, and the pH of the aqueous phase
was adjusted to approximately 12 with NaOH (10 N). The
product was extracted with diethyl ether (2 × 50 mL) and ethyl
acetate (2 × 30 mL). The extracts were combined, dried over
sodium sulfate, and filtered, and the filtrate was concentrated
under reduced pressure to give 0.37 g of the desired sulfone.
The free base was taken up in ethyl acetate and treated with
a solution of fumaric acid in methanol to produce a precipitate.
Filtration gave 25 (0.305 g, 46%). 1H NMR (400 MHz; DMSO-
d6): δ 7.86 (d, J ) 8.3 Hz, 1H), 7.20 (d, J ) 8.3 Hz, 1H); 7.09
(s, 1H); 7.01 (t, J ) 5.5 Hz, 1H), 6.49 (s, 2H); 4.34 (d, J ) 5.5
Hz, 2H), 3.66 (s, 4H); 3.26 (s, 3H). MS (ESI): 322 (M + H).
Anal: CHNS.
5-Meth yl-2-(m eth ylth io)a n ilin e (26). 2,5-Dimethylben-
zothiazole (10.44 g, 63.95 mmol) was slurried in ethylene glycol
(75 mL) and 10 N sodium hydroxide (75 mL). The reaction
mixture was heated to reflux under a nitrogen atmosphere.
After 4 h, the solution was cooled to 0 °C and treated with
concentrated hydrochloric acid to pH 7. The product was
extracted with diethyl ether (3 × 75 mL), dried over magne-
sium sulfate, and filtered, and the filtrate was concentrated
in vacuo to give 2.61 g of crude 2-amino-4-methylthiophenol.
The crude product (2.58 g) was dissolved in absolute ethanol
(50 mL), and the solution was cooled to 0 °C under a nitrogen
1
a precipitate. Filtration gave 20 (0.375 g, 74%). H NMR (400
MHz; DMSO-d6): δ 7.70 (dd, J ) 8.8 Hz, 6.6 Hz, 1H); 6.91 (br
s, 1H); 6.63-6.68 (m, 2H); 6.48 (s, 2H); 4.23 (d, J ) 5.3 Hz,
2H); 3.67 (s, 4H); 3.19 (s, 3H). MS. (ESI): 272 (M + H). Anal:
CHNS.
6-F lu or o-2-m eth ylth ioa n ilin e (21). 2,6-Difluoronitroben-
zene (1.0 g, 6.3 mmol) was stirred in ethanol (10 mL) and
treated with sodium methylmercaptan (0.44 g, 6.3 mmol) in
several portions over 5 min. After it was stirred for 2 h, the
mixture was concentrated in vacuo and the crude product was
chromatographed on silica gel (hexane:ethyl acetate (7:3) to
give 2-methylmercapto-6-fluoro-nitrobenzene (1.0 g). The ni-
trobenzene intermediate was reduced in ethanol (30 mL) using
5% palladium on carbon (0.3 g) and hydrogen at 50 psi for 2
h. The catalyst was removed by filtration through Celite, and
1
the solvent was evaporated to give 21 (0.69 g, 70%). H NMR
(300 MHz; DMSO-d6): δ 7.06 (d, J ) 7.8 Hz, 1H), 7.0 (dd, J )
11.2 Hz, 8.2 Hz, 1H), 6.6 (m, 1H), (5.1, br s, 2H), 2.35 (s, 3H).
The product was used in the subsequent reaction without
further analysis or purification.
2′-Meth ylth io-6′-flu or o-(an ilin om eth yl)im idazolin e Fu -
m a r a t e (22). Compound 21 (0.69 g, 4.37 mmol), 2-chloro-
methylimidazoline hydrochloride (0.6 g, 3.87 mL), 2,6-lutidine
(0.6 mL, 5.1 mmol), and phenol (0.5 g) were combined under
a nitrogen atmosphere, and the mixture was immersed in a
120 °C oil bath for 20 min. The mixture was diluted with water
(5 mL) and washed with methylene chloride (3 × 5 mL).
Sodium hydroxide (10 N) (2 mL) was added to the aqueous
phase, and the mixture was extracted with methylene chloride

2-(Anilinomethyl)imidazolines as Receptor Agonists
J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11 2237
atmosphere. Potassium tert-butoxide (2.29 g, 20.42 mmol) was
added portionwise, and the solution was stirred for 15 min.
Iodomethane (2.7 g, 19.02 mmol) in tetrahydrofuran (15 mL)
was added dropwise to the cold solution. After the addition
was complete, the slurry was stirred for 45 min. The volatiles
were removed by evaporation under reduced pressure. The
residue was taken up in deionized water (30 mL) and 10 N
sodium hydroxide (5 mL). The mixture was extracted with
diethyl ether (3 × 50 mL). The extracts were combined, washed
with saturated sodium chloride solution, dried over magnesium
sulfate, and filtered, and the filtrate was concentrated under
reduced pressure to give 2.64 g of 26. 1H NMR (400 MHz;
DMSO-d6): δ 7.11 (d, J ) 7.7 Hz, 1H), 6.54 (s, 1H), 6.38 (d, J
) 7.7 Hz, 1H); 5.14 (s, 2H), 2.26 (s, 3H), 2.16 (s, 3H). The
product was used in the subsequent reaction without further
analysis and purification.
2′-Me t h ylt h io-5′-m e t h yl-2-(a n ilin om e t h yl)im id a zo-
lin e F u m a r a te (27). Compound 26 (1.03 g, 6.74 mmol),
2-chloromethylimidazoline hydrochloride (0.522 g, 3.37 mmol),
and phenol (1.0 g) were combined, and the mixture was heated
at 145 °C for 1 h under a nitrogen atmosphere. After it was
cooled, the residue was taken up in deionized water (100 mL)
and ethyl acetate (75 mL). The aqueous layer was separated
and treated with 1 N sodium hydroxide to pH 12. The product
was extracted with ethyl acetate (3 × 40 mL). The extracts
were combined, dried over sodium sulfate, and filtered, and
the filtrate was concentrated under reduced pressure. The
residue was taken up in ethyl acetate and treated with a
solution of fumaric acid (1 equiv) in methanol to produce a
precipitate. Filtration gave 27 (0.67 g, 57%). 1H NMR (400
MHz; DMSO-d6): δ 7.24 (d, J ) 7.5 Hz, 1H), 6.41-6.58 (m,
4H), 5.98 (s, 1H), 4.21 (br s, 2H), 3.76 (s, 4H), 2.30 (s, 3H),
2.24 (s, 3H). MS (ESI): 236 (M + H).
2′-Meth ylsu lfon yl-5′-m eth yl-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (28). Compound 27 (0.560 g, 1.6 mmol) was
dissolved in methanol (20 mL) under a nitrogen atmosphere.
m-Chloroperoxybenzoic acid (0.736 g of 70-75% pure material)
was added portionwise. The mixture was stirred at room
temperature for 2 h. The mixture was poured into deionized
water (40 mL) and ethyl acetate (50 mL). The layers were
separated, and the pH of the aqueous layer was adjusted to
12 with 10 N NaOH. The product was extracted with diethyl
ether (2 × 75 mL), dried over magnesium sulfate, and filtered,
and the filtrate was concentrated under reduced pressure to
give 0.420 g of the free base. The free base was dissolved in
ethyl acetate and treated with a solution of fumaric acid in
methanol to produce a precipitate. Filtration gave 28 (0.458
g, 75%). 1H NMR (400 MHz; DMSO-d6): δ 7.53 (d, J ) 8.0 Hz,
1H), 6.62-6.68 (m, 3H), 6.47 (s, 2H), 4.26 (br s, 2H), 3.71 (s,
4H), 3.17 (s, 3H), 2.30 (s, 3H). MS (ESI): 268 (100%) (M + H).
Anal: CHNS.
methane (6.5 g, 45.8 mmol, 1.02 equiv). The ice-water bath
was removed, and the reaction mixture was allowed to stir at
room temperature overnight. The reaction mixture was fil-
tered, and the filtrate was concentrated in vacuo to give 9.6 g
of the crude product. Approximately one-half of the crude
product was purified by flash chromatography over silica gel
with hexanes:ethyl acetate (95:5) followed by hexanes:ethyl
acetate (3:1) as eluant to give 2.6 g of 30 as a yellow liquid.
1H NMR (300 MHz; DMSO-d6): δ 7.16 (d, J ) 8.5 Hz, 1H),
6.31 (d, J ) 2.5 Hz, 1H), 6.14 (dd, J ) 8.4 Hz, 2.6 Hz, 1H),
5.32 (br s, 2H), 3.67 (s, 3H), 2.20 (s, 3H).
2′-(Meth ylth io)-5′-m eth oxy-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (31). To a 25 mL round-bottom flask were
added 2-chloromethylimidazoline hydrochloride (93%) (0.6 g,
3.6 mmol), 30 (1.35 g, 7.19 mmol, 2.0 equiv), and phenol (0.88
g). The reaction mixture was heated at 135-145 °C with
stirring under a nitrogen atmosphere for 45 min. The oil bath
was removed, and the reaction mixture was allowed to cool at
room temperature. The reaction mixture was partitioned
between dichloromethane and water. The layers were sepa-
rated, and the pH of the aqueous phase was adjusted to
approximately 8 (litmus paper) with 1 N sodium hydroxide.
The basic aqueous phase was washed with dichloromethane.
The layers were separated, and the pH of the aqueous phase
was adjusted to 12 with 1 N sodium hydroxide. The aqueous
phase was extracted with diethyl ether (2×). The combined
diethyl ether extracts were dried over magnesium sulfate and
filtered, and the filtrate was concentrated in vacuo to give
0.544 g of the crude product as a gold-yellow oil. The free base
was purified by flash chromatography over silica gel with
dichloromethane:methanol:ammonium hydroxide (94:5:1) as
eluant to give 0.307 g of the free base as an oil, which partially
solidified to a white solid. The free base (0.307 g, 1.22 mmol)
and fumaric acid (0.142 g, 1.22 mmol, 1.0 equiv) were combined
and dissolved in hot methanol. The hot solution was filtered,
and the filtrate was allowed to cool at room temperature. The
title compound (31) (0.233 g; 18%) was filtered as a pale yellow
1
solid. H NMR (300 MHz; DMSO-d6): δ 7.30 (d, J ) 8.4 Hz,
1H), 6.47 (s, 2H), 6.27 (dd, J ) 8.4, 2.4 Hz, 1H), 6.19 (br t, J
) 5.9 Hz, 1H), 6.12 (d, J ) 2.3 Hz, 1H), 4.25 (d, J ) 6.0 Hz,
2H), 3.76 (s, 4H), 3.72 (s, 3H), 2.24 (s, 3H). MS (ESI): 252
(M+).
2′-Meth ylsu lfon yl-5′-m eth oxy-2-(a n ilin om eth yl)im id a -
zolin e F u m a r a te (32). 3-Chloroperoxybenzoic acid (57-86%,
assumed 86%) (0.22 g, 1.1 mmol, 2.0 equiv) was added
portionwise to a mixture of 31 (0.202 g, 0.55 mmol) and
methanol (20 mL) at room temperature with stirring under a
nitrogen atmosphere. Evaluation of the reaction by thin-layer
chromatography (dichloromethane:methanol:ammonium hy-
droxide (88:10:2) indicated the reaction was incomplete. Ad-
ditional 3-chloroperoxybenzoic acid was added to the reaction
mixture portionwise until thin-layer chromatography indicated
the reaction was complete. The reaction mixture was partially
concentrated under vacuum and diluted with water. The
aqueous mixture was washed twice with ethyl acetate. The
pH of the aqueous phase was adjusted to approximately 12
with 1 N sodium hydroxide. The basic aqueous phase was
extracted with ethyl acetate. The organic extract was dried
over magnesium sulfate and filtered, and the filtrate was
concentrated in vacuo to give 0.31 g of the free base as an off-
white solid. The free base (0.13 g, 0.46 mmol) and fumaric acid
(0.053 g, 0.46 mmol, 1.0 equiv) were dissolved in methanol,
and diethyl ether was added. The precipitated solid was
filtered, washed with diethyl ether, and dried under vacuum
at 70 °C to give 0.073 g (33%) of the title compound (32) as an
2-Am in o-4-m et h oxy-b en zen et h iol (29).22 To a 300 mL
round-bottom flask were added 5-methoxy-2-methylbenzothia-
zole (9.7 g, 54.1 mmol), sodium hydroxide (60 mL), and
ethylene glycol (60 mL). The reaction mixture was heated at
reflux with stirring under a nitrogen atmosphere for 3 h. The
oil bath was removed, and the reaction mixture was allowed
to cool at room temperature. The reaction mixture was washed
twice with diethyl ether and then cooled in an ice-water bath.
The pH of the cold aqueous phase was adjusted to ap-
proximately 3 (litmus paper) with concentrated hydrochloric
acid. The acidic aqueous phase was extracted twice with
diethyl ether. The combined organic extracts were washed with
water followed by saturated sodium chloride, dried over
magnesium sulfate, and filtered, and the filtrate was concen-
1
1
off-white solid. H NMR (300 MHz; DMSO-d6): δ 7.59 (d, J )
trated under vacuum to give 7.0 g (83%) of 29. H NMR (300
8.9 Hz, 1H), 6.74 (br t, J ) 5.3 Hz, 1H), 6.49 (s, 2H), 6.45 (br
dd, J ) 8.9, 2.1 Hz, 1H), 6.23 (br d, J ) 2.0 Hz, 1H), 4.25 (d,
J ) 5.2 Hz, 2H), 3.82 (s, 3H), 3.70 (s, 4H), 3.15 (s, 3H). MS
(ESI): 284 (M+).
MHz; CDCl3): δ 7.33 (d, J ) 8.5 Hz, 1H) 6.34 (m, 2H), 4.42
(br s, 2H), 3.79 (s, 3H).
5-Meth oxy-2-(m eth ylth io)a n ilin e (30). A solution of 29
(7.0 g, 45.1 mmol) in ethanol (100 mL) was cooled in an ice-
water bath and potassium tert-butoxide (5.6 g, 49.9 mmol, 1.1
equiv) was added portionwise via a powder addition funnel.
The reaction mixture was stirred under a nitrogen atmosphere
for 15 min. To the cold reaction mixture was added iodo-
2-Am in o-4-ch lor o-ben zen eth iol (33). This compound was
prepared according to the procedure described for 2-amino-4-
methoxy-benzenethiol by employing 5-chloro-2-methylben-
zothiazole (5.0 g, 27.2 mmol), 30% sodium hydroxide (30 mL),

2238 J ournal of Medicinal Chemistry, 2002, Vol. 45, No. 11
Hodson et al.
and ethylene glycol (30 mL). The reaction mixture was heated
2′-Meth ylsu lfon yl-4′-ch lor o-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (37). This compound was obtained as a
contaminant from a preparation of 3 in which sodium chloride
(at about 25 mol %) was present prior to oxidation. Oxone
oxidation of chloride to chlorine is well-documented.20 The free
base was isolated using reverse phase chromatography and
converted to the fumaric acid salt. The structure of the title
compound was determined via high-resolution mass spectrom-
etry (HRMS) and 1H NMR techniques. 1H NMR (300 MHz;
DMSO-d6): δ 7.62 (d, J ) 2.4 Hz, 1H), 7.57 (dd, J ) 8.9 Hz,
2.2 Hz, 1H), 6.84 (d, J ) 8.9 Hz, 1H), 6.79 (d, J ) 5.9 Hz, 1H),
6.5 (s, 2H), 4.2 (d, 5.0 Hz, 2H), 3.65 (s, 4H), 3.26 (s, 3H).
HRMS: 288.0559 (M + H).
8-Nitr oth ioch r om a n -4-on e (38). 3-[(2-Nitrophenyl)thio]-
propanoic acid21 (4.2 g, 18.5 mmol) was heated in POCl3 (21
mL) at 80 °C for 7 h. The mixture was concentrated in vacuo
to give an oil. The crude product was diluted with 30 mL of
CH2Cl2 and adsorbed onto silica gel. Chromatography on silica
using hexane/CH2Cl2 (1:2) gave 38 (1.8 g, 46%). The product
was used in the subsequent reaction without further purifica-
tion or analysis.
at reflux for 2.5 h and worked up to give 4.0 g (92%) of 33 as
1
an off-white solid. H NMR (300 MHz; DMSO-d6): δ 7.14 (d,
J ) 8.3 Hz, 1H), 6.71 (d, J ) 2.2 Hz, 1 H), 6.48 (dd, J ) 8.2,
2.2 Hz, 1H), 5.17 (br s, 2H). The product was used in the
subsequent reaction without further analysis or purification.
5-Ch lor o-2-(m eth ylth io)a n ilin e (34). To a 250 mL round-
bottom flask were added 33 (3.75 g, 23.5 mmol) and ethanol
(50 mL). The mixture was cooled in an ice-water bath, and
potassium tert-butoxide (2.9 g, 25.8 mmol, 1.1 equiv) was added
portionwise via a powder addition funnel. The cold reaction
mixture was stirred for 75 min. Iodomethane (3.5 g, 24.7 mmol,
1.05 equiv) was slowly added to the cold reaction mixture and
stirred for 30 min. The ice-water bath was removed, and the
reaction mixture was stirred at room temperature for 2 h. The
reaction mixture was filtered, and the filtrate was concentrated
1
in vacuo to give 2.5 g (61%) of 34 as a yellow liquid. H NMR
(300 MHz; DMSO-d6): δ 7.19 (d, J ) 8.2 Hz, 1H), 6.74 (d, J )
2.0 Hz, 1H), 6.55 (dd, J ) 8.2, 1.9 Hz, 1H), 5.49 (br s, 2H),
2.31 (s, 3H). The product was used in the subsequent reaction
without further analysis or purificaion.
8-Am in oth ioch r om a n (39).14 A solution of 38 (1.8 g, 8.6
mmol) in CH2Cl2 (40 mL)was treated with triflic anhydride
(1.8 mL, 10.6 mmol) and 2,6-di-tert-butyl-4-methylpyridine (2.2
g, 11 mmol) under nitrogen. The reaction mixture was heated
to reflux for 16 h. The mixture was washed with 1.0 N HCl,
and the layers were separated. The organic phase was dried
with sodium sulfate and filtered, and the filtrate was concen-
trated in vacuo. Chromatography on silica gel using hexane/
CH2Cl2 (1:1) gave the enol-triflate (1.0 g, 35%), which was used
without further purification. The enol-triflate was dissolved
in dry ethanol (60 mL) and treated with Pt oxide (140 mg)
and hydrogenated at 30 psi for 4 h. The catalyst was removed
by filtration, and the filtrate was concentrated in vacuo to give
39 (0.3 g, 60%). The product was used without further
purification.
2′-(Met h ylt h io)-5′-ch lor o-2-(a n ilin om et h yl)im id a zo-
lin e F u m a r a te (35). To a 50 mL round-bottom flask were
added chloromethylimidazoline hydrochloride (93%) (0.80 g,
4.8 mmol), 34 (2.0 g, 11.7 mmol, 2.4 equiv), and phenol (0.60
g). The reaction mixture was heated at 140 °C with stirring
under a nitrogen atmosphere for 50 min. The reaction mixture
was allowed to cool and then partitioned between water and
ethyl acetate. The layers were separated, and the pH of the
aqueous phase was adjusted to 9 with 1 N sodium hydroxide.
The basic aqueous phase was washed with ethyl acetate. The
layers were separated, and the pH of the aqueous phase was
adjusted to approximately 12 with 1 N sodium hydroxide. The
aqueous phase was extracted with ethyl acetate. The organic
solution was dried over magnesium sulfate and filtered, and
the filtrate was concentrated in vacuo to give 0.78 g of the
free base as a white solid. The free base (0.78 g, 3.05 mmol),
fumaric acid (0.354 g, 3.05 mmol, 1.0 equiv), and methanol
were combined, and the mixture was heated until the solids
fully dissolved. The hot solution was filtered, and the filtrate
was allowed to cool at room temperature and then placed in
the refrigerator. A white solid was filtered and rinsed with
diethyl ether to give 0.392 g (22%) of the title compound (35).
1H NMR (400 MHz; DMSO-d6): δ 7.30 (d, J ) 8.2 Hz, 1H)
6.68 (dd, J ) 8.1, 2.0 Hz, 1H), 6.57 (d, J ) 1.9 Hz, 1H), 6.45
(s, 2 H), 6.11 (br t, J ) 5.5 Hz, 1H), 4.14 (d, J ) 5.5 Hz, 2H),
3.69 (s, 4H), 2.33 (s, 3H). MS (ESI): 256 (M+). Anal: CHN.
2′-Meth ylsu lfon yl-5′-ch lor o-2-(a n ilin om eth yl)im id a zo-
lin e F u m a r a te (36). Methanol (10 mL) and 35 (0.373 g, 1.0
mmol) were combined in a round-bottom flask. To the stirred
suspension was added 3-chloroperoxybenzoic acid (57-86%,
assumed 86%) (0.40 g, 2.0 mmol, 2.0 equiv) portionwise at
room temperature. Thin-layer chromatography on silica gel
(dichloromethane:methanol:ammonium hydroxide, 88:10:2)
indicated that the reaction was incomplete. 3-Chloroperoxy-
benzoic acid was added portionwise until the reaction was
complete. The reaction mixture was partitioned between water
and ethyl acetate. The layers were separated, and the aqueous
phase was washed with ethyl acetate. The pH of the aqueous
phase was adjusted to approximately 12 with 1 N sodium
hydroxide. The basic aqueous phase was extracted with ethyl
acetate. The organic solution was dried over magnesium
sulfate and filtered, and the filtrate was concentrated under
vacuum to give 0.215 g of the free base as a white solid. The
free base (0.215 g, 0.75 mmol) and fumaric acid (0.086 g, 0.74
mmol, 1.0 equiv) were dissolved in methanol, and diethyl ether
was added to the solution until it became turbid. A white solid
was filtered, rinsed with diethyl ether, and dried under
vacuum. The product was recrystallized from ethanol, rinsed
with diethyl ether, and dried under vacuum to give 0.045 g
(11%) of the title compound (36) as a white solid. 1H NMR (300
MHz; DMSO-d6): δ 7.65 (d, J ) 9.0 Hz, 1H), 6.89 (m, 3 H),
6.51 (s, 2H), 4.22 (d, J ) 5.2 Hz, 2H), 3.66 (s, 4H), 3.21(s, 3H).
MS (ESI): 288 (M+). Anal: CHN.
N-(4,5-Dih yd r o-1H-im id a zol-2-ylm eth yl)-8-a m in oth io-
ch r om a n , 1,1-Dioxid e F u m a r a te (40). Compound 39 (0.3
g, 1.8 mmol), chloromethylimidazoline hydrochloride (0.28 g,
1.7 mmol), 2,6-lutidine (0.21 mL, 1.8 mmol), and phenol (0.2
g) were combined, and the mixture was heated for 15 min at
130 °C. The mixture was chromatographed on alumina (8:2
CH2Cl2:MeOH) to give 0.12 g of the N-alkylated intermediate.
The intermediate was dissolved in CH2Cl2 (4 mL) and treated
with meta-chloroperoxybenzoic acid (0.19 g of 85%). After 30
min, the mixture was stirred with water (2 mL) and 1 N NaOH
(1 mL). The organic phase was separated, dried (MgSO4), and
filtered. Fumaric acid (60 mg, 0.5 mmol) was added to the
filtrate. The solid that crystallized from solution was filtered
and dried in vacuo to give 90 mg (12%) of the desired product
(40). 1H NMR (300 MHz; DMSO-d6): δ 7.25 (t, J ) 8.0 Hz,
1H), 6.55 (t, J ) 9.0 Hz, 2H), 6.45 (s, 2H), 4.1 (d, J ) 5.5 Hz,
2H), 3.8 (s, 4H), 3.45 (dt, J ) 6.2 Hz, 2.3 Hz, 2H), 2.9 (t, J )
6.2 Hz, 2H), 2.22 (dt, J ) 6.2 Hz, 2.3 Hz, 2H). MS (ESI): 280
(M + H+). Anal: CHNS.
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