1-[2-methoxy-5-(3-phenylpropyl)]-2-aminopropane unexpectedly shows 5-HT2A serotonin receptor affinity and antagonist character

Article abstract of DOI:10.1021/jm0100739

Certain phenylethylamines, such as 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB; 1a), are high-affinity 5-HT₂ agonists. Previous structure - affinity studies have concluded that both the 2,5-dimethoxy substitution pattern and the nature of substituents at the 4-position are important determinants of high affinity. We recently demonstrated that replacement of the bromo group of DOB with a 3-(phenyl)propyl substituent results in retention of affinity and that, counter to established structure - affinity relationships, the 2,5-dimethoxy substitution pattern is no longer a requirement for the binding. The present investigation extends these findings by examining a series of analogues, 3, lacking a 5-methoxy group. It was additionally found that shifting the phenylalkyl substituent from the 4- to the 5-position (e.g., 4i) also results in retention of affinity. For example, 1-(2-methoxy-5-(3-phenylpropyl)-2-aminopropane (6; the α-methyl derivative of 4i) binds at 5-HT_2A receptors with high affinity (K_i = 13 nM) and possesses 5-HT_2A antagonist character. Thus, not only is the 2,5-dimethoxy substitution pattern not a requirement for the binding of certain phenylethylamines at 5-HT_2A receptors, the presence of a 4-position substituent (previously thought to serve as a modulator of affinity of DOB-like agents) is also not required. Striking differences in the 5-HT_2A binding requirements of the present compounds as compared to DOB-like agents suggest multiple substituent-dependent modes of binding.

Full text of DOI:10.1021/jm0100739

J . Med. Chem. 2001, 44, 3283-3291
3283
1-[2-Meth oxy-5-(3-p h en ylp r op yl)]-2-a m in op r op a n e Un exp ected ly Sh ow s 5-HT2A
Ser oton in Recep tor Affin ity a n d An ta gon ist Ch a r a cter
J agadeesh B. Rangisetty,† Małgorzata Dukat,† Cynthia S. Dowd,†,# Katharine Herrick-Davis,‡ Ann DuPre,‡
Sami Gadepalli,‡ Milt Teitler,‡ Curtis R. Kelley,§ Najam A. Sharif,§ and Richard A. Glennon*,†
Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University,
Richmond, Virginia 23298-0540, Center for Neuropharmacology and Neuroscience, Albany Medical College,
Albany, New York 12208, and Alcon Laboratories Inc., 6201 South Freeway, Fort Worth, Texas 76134-2099
Received February 13, 2001
Certain phenylethylamines, such as 1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB;
1a ), are high-affinity 5-HT2 agonists. Previous structure-affinity studies have concluded that
both the 2,5-dimethoxy substitution pattern and the nature of substituents at the 4-position
are important determinants of high affinity. We recently demonstrated that replacement of
the bromo group of DOB with a 3-(phenyl)propyl substituent results in retention of affinity
and that, counter to established structure-affinity relationships, the 2,5-dimethoxy substitution
pattern is no longer a requirement for the binding. The present investigation extends these
findings by examining a series of analogues, 3, lacking a 5-methoxy group. It was additionally
found that shifting the phenylalkyl substituent from the 4- to the 5-position (e.g., 4i) also results
in retention of affinity. For example, 1-(2-methoxy-5-(3-phenylpropyl)-2-aminopropane (6; the
R-methyl derivative of 4i) binds at 5-HT2A receptors with high affinity (Ki ) 13 nM) and
possesses 5-HT2A antagonist character. Thus, not only is the 2,5-dimethoxy substitution pattern
not a requirement for the binding of certain phenylethylamines at 5-HT2A receptors, the presence
of a 4-position substituent (previously thought to serve as a modulator of affinity of DOB-like
agents) is also not required. Striking differences in the 5-HT2A binding requirements of the
present compounds as compared to DOB-like agents suggest multiple substituent-dependent
modes of binding.
The 5-HT2 family of serotonin (5-HT) receptors is
reportedly involved in cardiovascular function and in a
wide array of central disorders including schizophrenia,
depression, anxiety, migraine, hallucinations, and eat-
ing disorders (reviewed1-4). An extensive body of litera-
ture is available on novel 5-HT2 antagonists (review-
ed2-4). A few 5-HT2 agonists are also available.2,4
Although 5-HT itself is a prototypical 5-HT2 agonist, it
lacks selectivity and is, consequently, of limited utility.
For the past 15 to 20 years, phenylethylamines such as
1-(4-bromo-2,5-dimethoxyphenyl)-2-aminopropane (DOB;
1a ) and related analogues such as its 4-iodo (DOI; 1b)
and 4-methyl (DOM; 1c) counterparts have been re-
agonists2 and have seen broad application in pharma-
cological investigations.
Structure-affinity relationships have been formu-
lated for DOB-like phenylethylamines,2,5 and the 2,5-
dimethoxy substitution pattern found in these ligands
was thought, until recently, to be important for 5-HT2
binding. The nature of the 4-position substituent is also
thought to be a major determinant of binding, and has
been shown to modulate affinity over a very broad
(>10000-fold) range.2,5 When the 4-position substituent
is -H or a polar group (e.g., -OH, -COOH) the compounds
bind with little (i.e., micromolar) to no affinity, whereas
halogen and small alkyl functions, e.g., C1-C6, impart
markedly enhanced affinity (e.g., refs 5 and 6). DOB
(1a ), for example, binds at 5-HT2A receptors with high
affinity (Ki ) 32 nM).7 It has been further shown,
however, that when alkyl chain length exceeds that of
a n-propyl group, agonist potency declines although
affinity is retained.2,8
Recently, we found that 1-(2,5-dimethoxy-4-(3-phen-
ylpropyl)phenyl)-2-aminopropane (1d ; Ki ) 30 nM)
binds at 5-HT2A receptors with an affinity comparable
to that of DOB (1a ) but that it behaves, at best, as a
partial agonist.7 More interestingly, we found that with
the 4-(3-phenylpropyl) substituent present, the struc-
ture-affinity relationships of 1d -like compounds sig-
nificantly deviate from established structure-affinity
requirements of DOB-like phenylethylamines. That is,
the presence of the 2,5-dimethoxy substitution pattern
is no longer a requirement for high affinity. For ex-
ample, removal of the 5-methoxy group of 1d , rather
1
garded as 5-HT2 (now 5-HT2A
)
serotonin receptor
* Address correspondence to R. A. Glennon, Ph.D. Phone: 804-828-
8487. Fax: 804-828-7404. E-mail:glennon@hsc.vcu.edu.
† Virginia Commonwealth University.
‡ Albany Medical College.
§ Alcon Laboratories Inc.
#
Present address: School of Medicine, University of Pennsylvania,
Philadelphia, PA 19104-6100.
10.1021/jm0100739 CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/30/2001

3284 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20
Rangisetty et al.
Ta ble 1. Physiochemical Data for Phenylalkylamines
than reducing or abolishing affinity as might have been
expected, actually enhanced affinity by severalfold (i.e.,
2; 5-HT2A Ki ) 8 nM).7
methoda yield (%) mp (°C)b
empirical formulac
3b
3c
3d
3e
3f
3g
3h
3i
A
A
A
A
-
A
B
C
A
-
-
-
B
B
B
A
A
A
A
-
A
C
A
41
44
55
24
41
33
72
28
29
48
56
46
62
57
22
46
52
66
19
61
32
32
29
168-169
167-169
161-163
163-165
138-140
161-163
161-163
167-169
189-191
189-190h
175-177
206-208
187-189i
165-167
196-197
175-177
178-180
169-171
181-183
144-146
181-183
182-184
209-210
C16H19NO‚C2H2O4
e
Because the 2-methoxy analogue 2 binds with higher
affinity than 1d , we embarked on a structure-affinity
investigation focusing on a series of aryl-substituted (2-
methoxyphenyl)-1-aminoethanes. We have already dem-
onstrated that the presence of a methyl group R to the
amine has little effect on 5-HT2A affinity.7 Hence, our
initial studies were conducted using derivatives of 3.
Because phenylethylamines are typically prone to rapid
metabolism in vivo, our intent was to prepare an
R-methyl analogue (i.e., a phenylisopropylamine) of one
of the more interesting compounds identified in this
study for use in future in vivo investigations. The
present study began with a determination of the affinity
of (2-methoxyphenyl)-1-aminoethane (3a ; i.e., 3, X ) H).
The 4-position of 3a was modified using several sub-
stituents shown to influence the affinity of 1d -type
compounds.7 During the course of this investigation it
became apparent that moving a 4-position substituent
to the 5-position impacted 5-HT2A binding. To further
study this effect, because 4-position substituents have
been previously thought to be a requirement for binding,
substituents used to explore the 4-position of 3 were
introduced to the 5-position to obtain a series of ana-
logues 4. Due to a paucity of compounds with selectivity
for 5-HT2A vs 5-HT2C receptors, the 5-HT2C receptor
affinities of the present compounds were also deter-
mined.
C17H21NO‚C2H2O4
d
C18H23NO‚C2H2O4
e
C19H25NO‚C2H2O4
f
C20H27NO‚C2H2O4
C18H28NO‚0.9C2H2O4
C17H21NO2‚C2H2O4
e
C20H23NO‚C2H2O4
C15H17NO‚C2H2O4
e
3j
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
g
C9H11BrNO‚C2H2O4
C9H12INO‚C2H2O4
C17H21NO2‚C2H2O4
C17H20BrNO2‚0.5C2H2O4
e
C16H19NO‚C2H2O4
e
C17H21NO‚C2H2O4
g
C18H23NO‚C2H2O4
C19H25NO‚C2H2O4
j
d
C20H27NO‚C2H2O4
C18H29NO‚C2H2O4
g
C20H23NO‚C2H2O4
e
C15H27NO‚C2H2O4
a
Method of preparation of the requisite aldehyde precursor (see
b
Experimental Section). All compounds were recrystallized from
MeOH/anhydrous Et2O. c All compounds analyzed correctly for C,
d
H, N within 0.4% of theory. Crystallized with 0.75 mol of H2O.
e Crystallized with 0.25 mol of H2O. f Crystallized with 1 mol of
H2O. g Crystallized with 0.5 mol of H2O. Lit.10 mp 186 °C. Lit.10
h
i
j
mp 189 °C. Prepared in the same manner as 3g.
aldehyde to the corresponding phenylethylamine is
described for 3d . The physicochemical properties of the
target amines, and the method of preparation used for
the synthesis of their intermediate aldehydes, is shown
in Table 1. Compounds 3b, 3c, 4g, and 4h were
prepared in a similar manner.
Meth od B. Phenylalkylamines 3h and 4e were
obtained from 4-(2-phenylethoxy)-2-methoxybenzalde-
hyde (13) and 5-(2-phenylethoxy)-2-methoxybenzalde-
hyde (14), respectively. The required aldehydes were
prepared by alkylating 4-hydroxy-2-methoxybenzalde-
hyde (7) and 5-hydroxy-2-methoxybenzaldehyde (8) with
2-bromo-1-ethylbenzene using Adogen-464 as a phase
transfer catalyst (Scheme 1). The above method was
adopted for the preparation of 5-(2-phenylethoxy)-4-
bromo-2-methoxybenzaldehyde (16) used in synthesis
of 4f. Synthesis of 16 began with bromination of
5-hydroxy-2-methoxybenzaldehyde (8) using Br2 and
SnCl4 to afford 15. Compound 15 was also prepared by
selective O-demethylation of 2,5-dimethoxy-4-bromobenz-
aldehyde followed by alkylation with 2-bromo-1-ethyl-
benzene to give the desired aldehyde.
Meth od C. The intermediate aldehyde, 17, for the
synthesis of 3i was obtained by Sonogashira cross-
coupling of 10 with 5-phenyl-1-pentyne in the presence
of a catalytic amount of palladium catalyst and copper
iodide. Compound 4m was prepared in like manner
(Table 1).
The phenylethylamine 3f was prepared by catalytic
reduction of alkyne 3i using Pd/C as catalyst (Scheme
1). Compounds 4a 10 and 4d 10 were synthesized accord-
ing to literature methods, and amine 4c was synthesized
by the iodination of 2-(2-methoxyphenyl)-1-aminoethane
(3a ) with iodine and silver sulfate.
Ch em istr y
The reported phenylethylamines 3 and 4 (Table 1)
were prepared from the appropriate 4- or 5-substituted
2-methoxybenzaldehydes via a Henry reaction to give
the corresponding nitrostyrenes, followed by reduction
of the nitrostyrenes with LiAlH4 or, where halogen was
present, with AlH3 (Scheme 1). The requisite benzalde-
hydes, which generally were not characterized, were
prepared by one of several methods.
Meth od A. The benzaldehydes required for prepara-
tion of 3d , 3e, 3g, 4i, 4j, 4k , and 4l, were obtained using
a Suzuki cross-coupling reaction between triflates (i.e.,
10 and 11) or commercially available 5-bromo-2-meth-
oxybenzaldehyde (9) with the appropriate 9-phenylalkyl-
9-borabicyclo[3.3.1]nonane7 in the presence of palladium
catalyst. In the case of 3j and 4n , the intermediate
aldehydes were obtained by cross-coupling of 10 or
5-bromo-2-methoxybenzaldehyde (9), respectively, with
phenylboronic acid. The triflates 10 and 11 were syn-
thesized from 4-hydroxy-2-methoxybenzaldehyde (7) or
5-hydroxy-2-methoxybenzaldehyde (8),9 respectively, in
the presence of triflic anhydride and pyridine. Prepara-
tion of the aldehydes is exemplified in the Experimental
Section for 12b (used in the synthesis of 3d ) and 12h
(used in the synthesis of 3j); a typical conversion of the
Compound 6 was prepared in a manner similar to
that which we have previously reported for several

1-[2-Methoxy-5-(3-phenylpropyl)]-2-aminopropane
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20 3285
Sch em e 1a
Sch em e 2a
a
Reagents: (a) (CF3CO)2O; (b) TiCl4, hydrocinnamoyl chloride;
(c) H2, 10% Pd/C; (d)15% NaOH.
438 nM) and resulted in about a 20-fold decrease in
affinity, whereas replacement of the benzylic methylene
of 3d with an ether oxygen (3h ; Ki ) 172 nM), or
introduction of unsaturation in the form of alkyne 3i
(Ki ) 295 nM), reduced affinity by an order of magnitude
or more. Finally, the 4-(3-propylphenyl) substituent of
3d was replaced by a 4-phenyl group to give 3j (Ki )
6720 nM) to result in a compound with significantly
reduced affinity.
On the basis that 1d presents a 5-oxygenated sub-
stituent whereas the inactive 3a does not, it was of
interest to determine the influence of 5-position sub-
stituents on the binding of 3a (Table 3). Introduction of
a 5-methoxy group (i.e., 5; Ki ) 2820 nM) resulted in
measurable affinity. O-Demethylation of 5 (4a ; Ki )
5960 nM) halved affinity, whereas replacement by a
bromo or iodo group (Ki ) 1000 nM and 700 nM for 4b
and 4c, respectively) only doubled or tripled affinity.
Ether analogues 4d and 4e (Ki ) 345 and 600 nM,
respectively) displayed somewhat enhanced, yet still
relatively modest, affinity. Most of these modifications
seemed to have a rather minimal influence on binding.
Attempting to rely on DOB-like structure-affinity
requirements, a 4-bromo group was added to 4e; the
resulting compound, 4f (Ki ) 91 nM), showed a 6-fold
increase in affinity. It might be noted that we have
previously shown that introduction of a 4-bromo group
enhances the affinity of 1-(2,5-dimethoxyphenyl)-2-
aminopropane (i.e., 1, X ) -H) and 2-(2,5-dimethoxy-
phenyl)-1-aminoethane (5) by >150-fold.7 It appears
that bromination of the ether analogue 4e does not
follow DOB-like SAR.
Taking a lead from the detrimental influence of the
oxygen ether in the 3-series compounds (i.e., comparing
ether 3h and its methylene counterpart 3d ), we replaced
the ether oxygen atom of 4e with a methylene group to
give 4i. Compound 4i (Ki ) 20 nM), which binds with
enhanced affinity, is a positional isomer of 3d (Ki ) 18
nM) and both bind with comparable affinity. Conse-
quently, we explored the effect of several other substit-
uents that we had examined in the 4-substituted series.
In contrast to what was observed in the 4-substituted
series, shortening of the alkyl chain of 4i by one or two
a
Reagents: (a) triflic anhydride, pyridine; (b) Suzuki; (c) (i)
MeNO2, (ii) LiAlH4; (d) phenylboronic acid, LiCl, Na2CO3, Pd-
(PPh3)4; (e) 2-Br-1-ethylbenzene, Adogen-464; (f) SnCl2, Br2; (g)
(i) MeNO2, (ii) AlH3; (h) 5-phenyl-1-pentyne, CuI, Et3N, PdCl2dppf;
(i) H2, 10% Pd/C.
structurally related compounds.7 1-(2-Methoxyphenyl)-
2-aminopropane (18) was protected by acylation of the
amine with trifluoroacetic anhydride to afford acetamide
19. The acetamide was acylated with hydrocinnamoyl
chloride under Friedel-Crafts conditions to afford the
ketone 20. Compound 20 was subjected to hydro-
genolytic conditions, and the product, 21, was depro-
tected to give the target compound 6 (Scheme 2).
Resu lts a n d Discu ssion
5-HT2A Ra d ioliga n d Bin d in g Stu d ies. The mono-
substituted methoxy compound 3a (Ki > 10000 nM)
showed little affinity for 5-HT2A receptors (Table 2). As
expected on the basis of our earlier findings,7 introduc-
tion of a 4-(3-phenylpropyl) substituent (3d ; Ki ) 18 nM)
enhanced affinity by >500-fold, and its affinity was
similar to that of its phenylisopropylamine counterpart
2 (Ki ) 8 nM).7 Shortening the alkyl chain of 3d (i.e.,
3b and 3c; Ki ) 23 and 46 nM, respectively) had
relatively little effect on affinity, whereas chain length-
ening of 3d to the 4-(4-phenylbutyl) and 4-(5-phenyl-
pentyl) analogues 3e and 3f (Ki ) 59 and 72 nM,
respectively) reduced affinity by 3- to 4-fold. The phenyl
ring of 3d was reduced to a cyclohexyl ring (3g; Ki )

3286 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20
Rangisetty et al.
Ta ble 2. Influence of 4-Position Substituents on the Binding of (2-Methoxyphenyl)-1-aminoethane (3a )
a
b
5-HT2A Ki, nM
5-HT2A Ki, nM
5-HT2C Ki, nM
2C/2A
ratioc
X
R
(SEM)
(SEM)
(SEM)
3a
3b
3c
3d
2e
3e
3f
3g
3h
3i
-H
-CH2-Ph
-H
-H
-H
-H
-Me
-H
-H
-H
-H
-H
-H
>10000
23 (4)
46 (12)
18 (6)
>10000
>10000
93 (12)
170 (12)
295 (23)
89
68 (6)
19 (5)
116 (17)
810 (140)
70 (18)
1520 (346)
-
4
4
16
11
1
<1
<1
5
d
-
-(CH2)2-Ph
-(CH2)3-Ph
-(CH2)3-Ph
-(CH2)4-Ph
-(CH2)5-Ph
-(CH2)3-cC6H11
-O-CH2CH2-Ph
-CtC-(CH2)3-Ph
-Ph
-
12 (3)
-
42 (19)
18 (2)
250 (95)
110(23)
240 (16)
4900 (840)
8
59 (13)
72 (27)
438 (140)
172 (40)
295 (133)
6720 (1818)
<1
<1
3j
a
b
5-HT2A sites labeled using [3H]ketanserin. 5-HT2A sites labeled using [3H]DOB. c 2C/2A ratio ) selectivity for 5-HT2A receptors (i.e.,
5-HT2C Ki ÷ 5-HT2A Ki value). Binding data not obtained. e Data for compound 2 were previously reported7 and are included only for
d
comparison.
Ta ble 3. Influence of 5-Position Substituents on the Binding of (2-Methoxyphenyl)-1-aminoethane (3a )
a
b
5-HT2A Ki, nM
5-HT2A Ki, nM
5-HT2C Ki, nM
2C/2A
ratioc
X
R
(SEM)
(SEM)
(SEM)
3a
5
-H
-H
-H
-H
-H
-H
-H
-H
-H
-H
-H
-H
-Me
-H
-H
-H
-H
-H
>10000
2820 (240)
5960 (1546)
1000 (270)
700 (110)
345 (52)
600 (54)
91 (9)
176 (33)
240 (14)
20 (3)
13 (2)
89 (31)
>10000
>10000
-
2
1
1
2
1
3
1
1
2
11
8
1
1
<1
<1
1
d
-OCH3
-OH
-Br
-
6400 (600)
4860 (260)
960 (125)
1640 (10)
410 (68)
1790 (52)
115 (30)
230 (7)
4a
4b
4c
4d
4e
4f
4g
4h
4i
6
4j
4k
4l
4m
4n
1330 (255)
208 (85)
211 (55)
255 (9)
440 (160)
35 (12)
-
-I
-O-CH2-Ph
-O-(CH2)2-Ph
-O-(CH2)2-Ph; 4-Br
-CH2-Ph
-(CH2)2-Ph
-(CH2)3-Ph
-(CH2)3-Ph
-(CH2)4-Ph
-(CH2)5-Ph
-(CH2)3-cC6H11
-CtC-(CH2)3-Ph
-Ph
-
435 (30)
220 (50)
110 (10)
71 (11)
150 (10)
198 (37)
205 (10)
2870 (80)
30 (11)
19 (7)
67 (20)
-
110 (20)
380 (150)
295 (35)
3460 (995)
760 (89)
-
1520 (390)
a
b
5-HT2A sites labeled using [3H]ketanserin. 5-HT2A sites labeled using [3H]DOB. c 2C/2A ratio ) selectivity for 5-HT2A receptors (i.e.,
d
5-HT2C Ki ÷ 5-HT2A Ki value). Binding data not obtained.
methylene units (i.e., 4h and 4g; Ki ) 240 and 176 nM,
respectively) decreased affinity by approximately 10-
fold. Parallel structural changes in the longer chain
analogues, however, seemed to result in roughly parallel
changes in affinity when the 3-series and 4-series
compounds were compared. That is, compared to the
3-phenylpropyl compounds 3d (Ki ) 18 nM) and 4i (Ki
) 20 nM), extension of the alkyl chain by one methylene
group (i.e., 3e; 4j) decreased affinity by about 3- to
4-fold, further extension by an additional methylene
(i.e., 3f; 4k ) had little effect, replacement of the benzylic
methylene by an ether oxygen (i.e., 3h ; 4e) decreased
affinity by about 10- to 30-fold, reduction of the phenyl
ring to a cyclohexyl ring (i.e., 3g; 4l) decreased affinity
by 20-fold, and introduction of an ethynyl group (i.e.,
3i; 4m ) reduced affinity by 15-fold. Replacement of the
entire group by a phenyl group (i.e., 3j; 4n ) decreased
affinity by >100-fold.
The significance of these parallel shifts is not fully
understood, but suggest that the longer chain members
of the two series might bind in such a manner that they
orient themselves in a roughly similar fashion, or that
their binding is influenced in a similar topographical
manner by receptor amino acid residues. Of particular
interest were the regioisomers 3d and 4i which bind
with nearly identical affinities. The structures of 3d and
4i were modeled using SYBYL, and conformational
searches identified the lowest energy conformers (3.58
and 3.45 kcal/mol for 3d and 4i, respectively). To
determine if 3d and 4i could bind at the receptor in such

1-[2-Methoxy-5-(3-phenylpropyl)]-2-aminopropane
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20 3287
a manner that they interact with common amine and
aromatic binding sites, the lowest energy conformers
from each of the sets were superimposed using MUL-
TIFIT. A good superimposition was achieved (rms )
0.050). Calculated energies of the conformers obtained
from the superimposition study (3.73 and 3.66 kcal/mol,
respectively) were not very different from their starting
energies. Calculated distances between the amine
nitrogen atom and the phenylethylamine centroid (C1)
were 5.13 and 5.17 Å for 3d and 4i, respectively, and
the distances between the amine and the distant
aromatic centroid (C2) were 9.26 Å for 3d and 9.25 Å
for 4i. The calculated C1-C2 distances were 6.49 and
6.56 Å, respectively. It would seem possible then, at
least in theory, for the terminal amine and the distant
phenyl ring of both compounds to avail themselves of
common contact points on the receptor structure.
As originally planned, we synthesized an R-methyl or
phenylisopropylamine analogue of one of the phenyl-
ethylamines. Specifically, we selected 4i, the highest
affinity member of the series, and prepared its R-methyl
analogue 6. Compound 6, a positional isomer of 2, was
found to bind with an affinity (Ki ) 13 nM; Table 3)
similar to that of its desmethyl counterpart (4i; Ki ) 20
nM) and comparable to that of 2 (Ki ) 8 nM; Table 2).
F igu r e 1. Inhibition of 5-HT-induced PI turnover by 6 in A7r5
cells. The figure depicts results from three separate experi-
ments (mean ( SEM), each conducted in duplicate. The
concentration of 5-HT was 10 µM in these experiments.
5-HT2C Ra d ioliga n d Bin d in g Stu d ies. Most of the
compounds in Tables 2 and 3 bind at 5-HT2C receptors
with an affinity comparable to, up to about 10-fold lower
than, what they display at 5-HT2A receptors. With the
exception of 3d (16-fold 5-HT2A selective), none of the
compounds displayed >11-fold selectivity for one popu-
lation over the other. Given the high amino acid
sequence homology between 5-HT2A and 5-HT2C recep-
tors,11 this lack of selectivity is not surprising.
F u n ction a l Activity. 5-HT2 agonists typically bind
with higher affinity at sites labeled by a 5-HT2 agonist
(e.g., [3H]DOB, [125I]DOI) than at sites labeled by a
5-HT2 antagonist (e.g., [3H]ketanserin), whereas an-
tagonists typically bind with similar affinity regardless
of the type of radioligand employed. Hence, a compari-
son of affinities at the differently labeled sites serves
as a preliminary indicator of functional activity. Most
of the compounds in Tables 2 and 3 failed to show
markedly higher affinity for agonist-labeled (i.e., [3H]-
DOB-labeled) sites as compared to antagonist-labeled
(i.e., [3H]ketanserin-labeled) sites suggesting that they
might be 5-HT2 antagonists. In particular, 6 binds with
nearly equal affinity at agonist-labeled 5-HT2A sites
(Ki ) 19 nM) and antagonist-labeled 5-HT2A sites (Ki )
13 nM). The R-methyl analogue 6 was selected for
examination in a PI hydrolysis assay to obtain further
evidence for possible 5-HT2A antagonist activity. Sero-
tonin (5-HT) stimulated PI turnover and accumulation
of total [3H]-IPs in A7r5 cells was measured in a
concentration-dependent manner. The potency of 5-HT
(EC50 ) 329 ( 38 nM; n ) 4) and its intrinsic activity
(IA ) 1.0) compare well with results previously reported
by Doyle et al.12 At a concentration of 10 µM, compound
6 was found to produce little more than baseline effects
in this assay. Compound 6 was evaluated as an antago-
nist, and was found to antagonize 5-HT-induced ac-
cumulation of total [3H]-IPs in a concentration-depend-
ent manner (Figure 1) with an equilibrium dissociation
constant, Ki, of 244 ( 45 nM (n ) 3). A known
F igu r e 2. Structures of sarpogrelate and one of its metabo-
lites and of trans-4-([3Z]3-(2-dimethylaminoethyl)oxyimino-3-
(2-fluorophenyl)propen-1-yl]phenol (SR 46349B).
antagonist of 5-HT-induced PI turnover, RS-102221,
was used as control (Ki ) 34 ( 7 nM; n ) 3; data not
shown). It would appear, then, that compound 6 pos-
sesses 5-HT2A antagonist character.
Compound 6 bears a remote structural similarity to
certain other 5-HT2 antagonists, in particular sarpogre-
late and SR 46349B (Figure 2). Sarpogrelate (IC50 ca.
150 nM) possesses a nonessential ester function and its
hydroxy metabolite binds at 5-HT2 receptors with
enhanced affinity (IC50 ) 12.5 nM).13 Although newer
sarpogrelate analogues have been reported with even
higher affinity, they have in common a 2-(2-phenyleth-
yl)phenoxypropylamine moiety; that is, they are phen-
oxypropylamines, not phenylethylamines.14 SR 46349B
(5-HT2A IC50 ) 5.8 nM; 5-HT2C IC50 ) 120 nM)15,16 is
another example of a nonphenylethylamine 5-HT2 an-
tagonist containing two phenyl rings separated by an
alkyl chain. Although each of these agents is structur-
ally distinct, there is insufficient evidence to eliminate
the possibility that compounds such as 6, the sarpogre-
late analogues, and SR 46349B might somehow bind in

3288 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20
Rangisetty et al.
Ta ble 4. Calculated Distances for Selected Atoms in the
MULTIFIT Superimposition of 3d , 4i, and SR 46349B
ships established for the binding of phenylethylamines
at 5-HT2 receptors are no longer valid. It might be noted,
however, that those compounds violating these previ-
ously established relationships seem to lack activity as
full agonists. Thus, the possibility exists that agonist
phenylethylamines and partial agonist (or antagonist)
phenylethylamines are binding at 5-HT2A receptors in
a different manner. Furthermore, modeling studies with
3d and 4i indicate that it is energetically feasible for
the two compounds to assume conformations that result
in nearly identical amine-to-centroid distances, and that
these structures can assume conformations similar to
that of a known 5-HT2 antagonist. Nevertheless, con-
tinued effort is required to definitively establish whether
these novel compounds bind at 5-HT2 receptors in a
manner similar to, or different than, that of DOB-like
agonists.
energy after
MULTIFIT
(kcal/mol)
distances (Å)b
energya
(kcal/mol)
N-C1 N-C2 C1-C2
3d
4i
3.58
3.45
9.79
3.63
4.37
9.97
5.16
5.19
5.16
10.04
10.03
10.11
6.68
6.70
6.76
SR 46349B
a
Energy of lowest energy conformer prior to performing MUL-
b
TIFIT. C1 for 3d and 4i is defined as the aromatic centroid of
the phenylethylamine ring whereas C2 is the centroid of the
distant phenyl ring. For SR 46349B, C1 is the centroid of the
fluorine-containing ring whereas C2 is the centroid of the hydroxyl-
containing ring; N is the dimethylamino nitrogen atom.
a similar fashion at 5-HT2 receptors. To explore this a
bit further, we identified the lowest energy conformer
of SR 46349B (9.79 kcal/mol). Using MULTIFIT, this
conformer was superimposed on 3d and 4i. The calcu-
lated interatom (i.e., amine and aryl centroid) distances
are shown in Table 4. Using FIT ATOMS, superimposi-
tion of SR 46349B with 3d or 4i gave rms values of 0.037
and 0.044, respectively. Thus, there exists a reasonable
possibility that the 3-(phenyl)propyl-substituted phen-
ylethylamines could bind at 5-HT2 receptors in a man-
ner that mimics SR 46349B. These are fairly flexible
molecules, and a number of low energy conformations
exist. Nevertheless, the ability to mimic the general
structure of known 5-HT2 antagonists, such as SR
46349B, might provide one explanation for the shift in
functional activity of certain phenylalkylamines from
agonist to antagonist when the 3-(phenyl)propyl sub-
stituent is present.
Exp er im en ta l Section
A. Syn th esis. Melting points were determined with a
Thomas-Hoover melting point apparatus and are uncorrected.
Proton magnetic resonance (1H NMR) spectra were obtained
with a Varian Gemini 300 spectrometer, using tetramethyl-
silane as an internal standard. Infrared spectra were recorded
on
a Nicolet 5ZDX FT-infrared spectrometer. Elemental
analysis was performed by Atlantic Microlab, Inc., and deter-
mined values are within 0.4% of theory. Thin-layer chroma-
tography (TLC) was performed using silica gel-coated GHIF
plates (250 µ, 2.5 × 10 cm, Analtech, Inc., Newark, DE). Dry
THF was obtained by distillation over sodium metal and
benzophenone. Dry CH2Cl2 was obtained by distillation over
phosphorus pentoxide (P2O5).
2-(2-Met h oxy-4-(3-p h en ylp r op yl)p h en yl)-1-a m in oet -
h a n e Oxa la te (3d ). A solution of 12b (0.30 g, 1.10 mmol),
NH4OAc (0.09 g, 1.16 mmol), and MeNO2 (10 mL) was heated
at reflux under a N2 atmosphere for 3 h. The solvent was
removed under reduced pressure. The resultant residue was
extracted with CH2Cl2 (2 ×15 mL), washed with H2O (30 mL),
and dried (MgSO4), and the solvent was removed under
reduced pressure to give an oil. The oil in dry THF (20 mL)
was added in a dropwise manner to a suspension of LiAlH4
(0.10 g, 2.64 mmol) in dry THF (20 mL). The reaction mixture
was heated at reflux for 5 h under a N2 atmosphere, then
cooled to 0 °C. The hydride reagent was decomposed by
addition of H2O (1 mL) and 15% NaOH (1 mL). The resulting
white solid was collected by filtration and washed with dry
THF (25 mL). The solvent was evaporated under reduced
pressure to give a yellow oil. The oil was purified by column
chromatography (CH2Cl2/MeOH, 9:1) and converted to an
oxalate salt which was recrystallized from MeOH/anhydrous
Et2O to give 0.24 g (55%) of 3d as a white solid: mp 161-163
°C. 1H NMR (DMSO-d6) δ: 8.3 (s, 3H, NH3+), 7.4-7.6 (m, 5H,
ArH), 7.1 (d, 1H, ArH), 6.9 (s, 1H, ArH), 6.8 (d, 1H, ArH), 3.7
(s, 3H, OCH3), 2.9 (t, 2H, CH2), 2.7 (t, 2H, CH2), 2.5 (m, 4H,
2 × CH2), 1.9 (t, 2H, CH2). Anal. (C18 H23NO‚C2H2O4‚0.75 H2O)
C, H, N.
2-(2-Me t h o x y -4-(5-p h e n y lp e n t y l)p h e n y l)-1-a m in o -
eth a n e Oxa la te (3f). A solution of 3i (0.20 g, 0.68 mmol) in
MeOH (50 mL) was hydrogenated over 10% Pd/C (0.15 g, 1.43
mmol) for 3 h at 40 psi. The reaction mixture was filtered,
and the solvent was removed under reduced pressure to give
a white solid, which was then converted to an oxalate salt.
The oxalate salt was recrystallized from MeOH/anhydrous
Et2O to give 0.10 g (41%) of the title compound: mp 138-140
°C. 1 H NMR (CD3OD) δ: 6.8-7.2 (m,5H,ArH) 6.4-6.6 (m, 3H,
ArH), 3.80 (s, 3H, OCH3), 2.9 (t, 2H, CH2), 2.7 (t, 2H, CH2),
2.3 (m,4H, 2CH2) 1.8 (m, 4H, 2CH2). Anal. (C20 H27NO‚C2H2O4‚
H2O) C,H,N.
Su m m a r y. The purpose of the present investigation
was not to develop novel 5-HT2 antagonists; indeed,
numerous high-affinity and potent 5-HT2 antagonists
already are known.4 Rather, the intended purpose of
this study was to redefine the structure-affinity re-
quirements for the binding of simple phenylethylamines
at 5-HT2 receptors. Phenylethylamines such as DOB
(1a ) and DOI (1b) are widely used 5-HT2 agonists, and
it has nearly become dogma that the presence of 2,5-
dimethoxy substitution is a critical requirement for
high-affinity binding. In contrast to established struc-
ture-activity requirements, we have recently demon-
strated that the 2,5-dimethoxy substitution pattern can
no longer be considered a requirement for phenylethyl-
amines to bind with high affinity at 5-HT2A receptors
or to produce 5-HT2 agonist action.7 The present study
extends these findings and provides further evidence in
support of this concept. Compounds such as 4i and 6
are quite unusual in that they unexpectedly bind at
5-HT2A receptors. Not only do these compounds lack the
2,5-dimethoxy substitution pattern, they are the first
simple phenylethylamines to bind at 5-HT2A receptors
with low nanomolar affinity even though they lack a
4-position substituent. Moreover, the binding data
obtained using [3H]DOB as radioligand indicates that
many of these compounds should act as 5-HT2A antago-
nists; this was verified for compound 6 using a func-
tional assay. Although the antagonist potency of 6 is
unremarkable, what is remarkable is that it binds at
5-HT2A receptors with high affinity and that it is not a
5-HT2A agonist. The present findings, coupled with the
results of an earlier study,7 argue that when a phenyl-
alkyl substituent is present, structure-affinity relation-
2-(2-Me t h oxy-4-(2-p h e n yle t h oxy)p h e n yl)-1-a m in o-
eth a n e Oxa la te (3h ). The title compound was prepared as
described for 3d using 13 as a starting material. The oxalate

1-[2-Methoxy-5-(3-phenylpropyl)]-2-aminopropane
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20 3289
salt (0.80 g, 72%) was obtained as white solid after recrystal-
lization from MeOH/anhydrous Et2O: mp 161-163 °C. 1H
NMR (CDCl3, free base) δ: 7.2-7.3 (m, 5H, ArH), 7.0 (d, 1H,
ArH), 6.4 (d, 1H,ArH), 4.1 (t, 2H, CH2), 3.7 (s, 3H, OCH3), 3.0
(t, 2H, CH2), 2.7-2.9 (m, 4H, 2CH2). Anal. (C17H21NO2‚C2H2O4)
C, H, N.
(d, 1H, ArH), 7.05 (dd, 1H, ArH), 7.16-7.31 (m, 5H, Ar-H),
7.44 (bs, 1H, NH). Aqueous 15% NaOH (20 mL) was added to
a solution of 21 (0.41 g, 1.08 mmol) in MeOH (20 mL), and
the reaction mixture was heated at reflux for 2 h then allowed
to cool to room temperature. The MeOH was removed under
reduced pressure, and the aqueous portion was extracted with
Et2O (3 × 50 mL). The combined organic portion was dried
(MgSO4), and solvent was evaporated under reduced pressure
to give a clear oil. The oil was triturated with ethereal HCl to
give 0.15 g (43%) of the salt as a white powder: mp 86-88
°C. 1H NMR (D2O) δ: 1.08 (d, 3H, CH3), 1.65-1.69 (m, 2H,
CH2), 2.31 (t, 2H, CH2), 2.40 (t, 2H, CH2), 2.64 (dd, 1H, CH2),
2.81 (dd, 1H, CH2), 3.42-3.48 (m, 1H, CH), 3.62 (s, 3H, OCH3),
6.64 (d, 1H, ArH,), 6.78-6.80 (m, 2H, ArH), 7.01-7.16 (m, 5H,
ArH). Anal. (C19H26ClNO‚HCl‚0.25 H2O) C, H, N.
2-(2-Meth oxy-4-(5-p h en yl-1-p en tn yl)p h en yl)-1-a m in o-
eth a n e Oxa la te (3i). Compound 3i was prepared in 28% yield
as described for 3d using 17 as starting material. Compound
3i was obtained as white solid: mp 167-169 °C (MeOH/
1
anhydrous Et2O). H NMR (CD3OD) δ: 6.6-7.2 (m, 5H, ArH)
6.1-6.3 (m, 3H, ArH), 3.90 (s, 3H, OCH3), 2.9 (t, 2H, CH2),
2.7 (t, 2H, CH2), 2.4-2.6 (m, 6H, 3CH2). Anal. (C20 H23NO‚
C2H2O4‚0.25 H2O) C, H, N.
2-(2-Meth oxy-5-br om op h en yl)-1-a m in oeth a n e Oxa la te
(4b). A solution of 5-bromo-2-methoxybenzaldehyde (9) (0.25
g, 1.16 mmol), NH4OAc (0.10 g, 1.29 mmol), and MeNO2 (10
mL) was heated at reflux under a N2 atmosphere for 4 h. The
solvent was removed under reduced pressure, and the residue
was extracted with CH2Cl2 (2 × 20 mL). The combined organic
portion was washed with H2O (20 mL) and dried (MgSO4), and
the solvent was evaporated under reduced pressure. The
resultant solid was recrystallized from 2-PrOH: mp 121-123
°C. 1H NMR (CDCl3) δ: 8.2 (d, 1H, CH), 7.9 (d, 1H, CH), 6.8-
7.6 (m, 3H, ArH), 3.97 (s, 3H, OCH3). A slurry of AlCl3 (0.10
g, 0.80 mmol) in dry THF (10 mL) was cooled in an ice bath,
and LiAlH4 (0.06 g, 1.60 mmol) was slowly added under a N2
atmosphere. A solution of above intermediate nitrostyrene
(0.20 g, 0.75 mmol) in dry THF (15 mL) was added in a
dropwise manner to the above solution at 0 °C. The mixture
was allowed to stir overnight at room temperature. The
reaction mixture was cooled in an ice bath, and excess alane
was destroyed by successive addition of H2O (1 mL), 10%
NaOH (1 mL). The resulting white solid was collected by
filtration and washed with dry THF (25 mL). The solvent was
evaporated under reduced pressure to give a yellow oil. The
oil was purified by column chromatography (CH2Cl2/MeOH,
10:1) and converted to an oxalate salt. The oxalate salt was
recrystallized from MeOH/anhydrous Et2O to give 0.14 g (56%)
2-Me t h o x y -4-(t r iflu o r o m e t h a n e s u lfo n y lo x y )b e n z-
a ld eh yd e (10). Trifluoromethanesulfonic anhydride (1.50 mL,
8.88 mmol) in CH2Cl2 (25 mL) was added in a dropwise manner
to a solution of 4-hydroxy-2-methoxybenzaldehyde (7) (1.18 g,
7.76 mmol) in CH2Cl2 (25 mL) and pyridine (1 mL) at 0 °C
under a N2 atmosphere. The reaction mixture was brought to
room temperature and allowed to stir for 2 h. The solvents
were removed under reduced pressure to give a semisolid
material. Purification by column chromatography (hexanes/
1
EtOAc, 5:1) gave 1.10 g (47%) of 10. H NMR (CDCl3) δ: 3.98
(s, 3H, OCH3), 6.91 (s,1H, ArH), 6.96 (d, 1H, ArH) 7.93 (d, 1H,
ArH), 10.43 (s, 1H, CHO).
2-Me t h o x y -5-(t r iflu o r o m e t h a n e s u lfo n y lo x y )b e n z-
a ld eh yd e (11). Compound 11 was obtained as a semisolid
material in 86% yield by reaction of 5-hydroxy-2-methoxyben-
zaldehyde (8)9 with trifluoromethanesulfonic anhydride in
1
manner similar to that described for 10. H NMR (CDCl3) δ:
3.98(s, 3H, OCH3), 6.92 (s, 1H, ArH), 6.96 (d, 1H, ArH), 7.94
(d, 1H, ArH), 10.43 (s, 1H, CHO).
Met h od A. 2-Met h oxy-4-(3-p h en ylp r op yl)b en za ld e-
h yd e (12b). A solution of 9-phenyl-propyl-9-BBN (prepared
from allylbenzene and 9-BBN at room temperature for 3 h)7
(3.70 mmol) was added to a mixture of 10 (0.80 g, 2.82 mmol),
THF (20 mL), 3 M NaOH (3 mL), and PdCl2(dppf) (0.08 g, 0.08
mmol) under a N2 atmosphere and heated at reflux for 6 h.
The reaction mixture was cooled to room temperature, and the
solvent was removed under reduced pressure. The remaining
residue was extracted between EtOAc (4 × 25 mL) and H2O.
The organic portion was dried (MgSO4), and the solvent was
removed under reduced pressure to give a yellow oil. Kugelrohr
distillation of the oil gave a colorless oil (0.60 g, 84%) at 0.06
1
of the title compound: mp 175-177 °C. H NMR (CDCl3, free
base) δ: 7.2-7.3 (m, 2H, ArH), 6.7 (d, 1H, ArH), 3.78 (s, 3H,
OCH3), 2.9 (t, 2H,CH2), 2.72 (t, 2H, CH2), 2.58 (s, 2H, NH2).
Anal. (C9H11BrNO‚C2H2O4‚0.5H2O) C, H, N.
2-(2-Met h oxy-5-iod op h en yl)-1-a m in oet h a n e Oxa la t e
(4c). Following the general method of Sy,17 2-(2-methoxy-
phenyl)ethylamine (1.00 g, 6.61 mmol) was added to a mixture
of I2 (3.35 g, 13.22 mmol) and Ag2SO4 (4.12 g, 13.22 mmol) in
absolute EtOH (50 mL) at room temperature. The mixture was
allowed to stir for 20 h and was filtered. The filtrate was
evaporated to dryness under reduced pressure. The residue
was dissolved in CH2Cl2 (50 mL) and washed with 5% NaOH
solution (40 mL) then with H2O (50 mL). The organic portion
was dried (MgSO4) and evaporated to dryness. The residue
was purified by column chromatography (CH2Cl2/MeOH,
20:1) to give an oil, and the oil was treated with oxalic acid.
The oxalate salt was recrystallized from MeOH/anhydrous
Et2O to give 1.10 g (46%) of 4c: mp 206-208 °C.1 H NMR
(CDCl3 , free base) δ: 7.3-7.4 (m, 2H, ArH), 6.5 (d, 1H, ArH),
3.71 (s, 3H, OCH3), 2.85 (t, 2H,CH2), 2.66 (t, 2H, CH2), 2.01
(s, 2H, NH2). Anal. (C9 H12 INO‚C2H2O4) C, H, N.
(()1-[2-Met h oxy-5-(3-p h en ylp r op yl)p h en yl]-2-a m in o-
p r op a n e Hyd r och lor id e (6). A mixture of 20 (0.45 g, 1.14
mmol), AcOH (45 mL), HClO4 (70%, 0.20 mL), and 10% Pd/C
(0.20 g) was shaken on a Parr hydrogenator under 45 psi of
hydrogen at room temperature for 5.5 h. The reaction mixture
was filtered; the filtrate was diluted by the addition of H2O
(30 mL), and the solution was extracted with CH2Cl2 (3 × 40
mL). The combined organic portion was extracted with satu-
rated NaHCO3 (3 × 40 mL) and dried (MgSO4). Evaporation
and azeotropic removal of the residual AcOH with hexanes
gave 0.43 g (99%) of 21 as a white solid: mp 65-67 °C. 1H
NMR (CDCl3): δ 1.25 (d, 3H, CH3), 1.89-1.97 (m, 2H, CH2),
2.58 (t, 2H, CH2), 2.64 (t, 2H, CH2), 2.83 (d, 2H, CH2), 3.84 (s,
3H, OCH3), 4.06-4.15 (m, 1H, CH), 6.81 (d, 1H, ArH), 6.93
1
mmHg (oven temp: 185-195 °C). H NMR (CDCl3) δ: 10.41
(s, 1H, CHO), 7.75 (d, 1H, ArH), 7.20-7.30 (m, 5H, ArH), 6.81
(s, 1H, ArH), 6.70 (s, 1H, ArH), 3.90 (s, 3H, OCH3), 2.65-2.72
(m, 4H, CH2-CH2), 1.94-2.04 (m, 2H, CH2). Aldehyde 12b was
used in the preparation of 3d .
2-Meth oxy-4-p h en ylben za ld eh yd e (12h ). Phenylboronic
acid (0.30 g, 2.46 mmol) was added to a mixture of 10 (0.50 g,
1.76 mmol), THF (20 mL), LiCl (0.01 g), 2 M Na2CO3 solution
(2.0 mL), and Pd(PPh3)4 (0.03 g) under N2 atmosphere and
heated at reflux for 10 h. The reaction mixture was cooled to
room temperature, and the solvent was removed under re-
duced pressure. The remaining residue was extracted between
EtOAc (4 × 25 mL) and H2O. The organic portion was dried
(MgSO4), and the solvent was removed under reduced pressure
to give an oil. The oil was purified by column chromatography
(hexanes/EtOAc, 40:1) to give 0.30 g (79%) of the title
compound. 1H NMR (CDCl3) δ: 10.48 (s, 1H, CHO), 7.88 (d,
1H, ArH), 7.4-7.6 (m, 5H, ArH), 7.1-7.2 (s, 2H, ArH), 3.99
(s, 3H, OCH3). Aldehyde 12h was used in the synthesis of 3h .
Met h od B. 2-Met h oxy-4-(2-p h en ylet h oxy)b en za ld e-
h yd e (13). Following the general procedure of Leeson et al.,18
NaOH (0.32 g, 8.00 mmol) in H2O (25 mL) was added to a
stirred suspension of 4-hydroxy-2-methoxybenzaldehyde (7)
(1.00 g, 6.57 mmol), 2-bromo-1-ethylbenzene (1.30 g, 7.00
mmol), and Adogen-464 (1.00 g) in CH2Cl2 (25 mL) at room
temperature. After 8 h, the organic portion was removed,
washed with H2O (25 mL) and saturated NaCl solution, and
dried (MgSO4), and the solvent was evaporated under reduced

3290 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20
Rangisetty et al.
1
pressure to give 1.20 g (69%) of 13 as an oil. H NMR (CDCl3)
CH2Cl2 portion was washed with H2O (3 × 25 mL). The
aqueous portion was washed with CH2Cl2 (3 × 25 mL). The
combined organic portions were washed with 5% HCl, H2O,
saturated NaHCO3, saturated NaCl (3 × 25 mL each), then
dried (MgSO4). Solvent was removed under reduced pressure
to give 0.9 g of a beige solid. Recrystallization from absolute
EtOH gave 0.48 g (24%) of the desired compound: mp 94-96
δ: 10.30 (s, 1H, CHO), 7.6 (d, 1H, ArH), 7.0-7.5 (m, 5H, ArH),
6.4 (d, 1H, ArH), 6.3 (s, 1H, ArH), 4.1 (t, 2H, CH2), 3.7 (s,3H,
OCH3), 3.4 (t, 2H,CH2). Compound 13 was used without
further characterization in the synthesis of 3h .
4-Br om o-5-h ydr oxy-2-m eth oxyben zaldeh yde (15): Meth -
od I. According to a procedure described by Ulrich et al.,9
concentrated H2SO4 (20 mL) was slowly added to 4-bromo-2,5-
dimethoxybenzaldehyde19 (2.5 g, 10.20 mmol) with ice cooling,
and the mixture was heated at 50-55 °C for 48 h. The reaction
mixture was poured into ice, and precipitated oil was extracted
with Et2O (4 × 25 mL). The Et2O solution was extracted with
5% NaOH solution (75 mL), and the aqueous portion was
acidified with dilute HCl and then extracted with Et2O (4 ×
30 mL). The combined Et2O portions were dried (MgSO4), and
evaporation of the solvent gave 1.3 g (55%) of 15. 1H NMR
(CDCl3) δ: 10.35 (s, 1H, CHO). 7.45 (s, 1H, ArH), 7.1 (s, 1H,
ArH), 3.88 (s, 3H, OCH3).
Meth od II. Anhydrous SnCl4 (3.65 g, 14.00 mmol) was
slowly added to a solution of 5-hydroxy-2-methoxybenzalde-
hyde (8)9 (2.00 g, 13.15 mmol) in CH2Cl2 (50 mL); this was
followed by the dropwise addition of Br2 (2.40 g, 15.01 mmol)
over a 30-min period. The resulting solution was heated at
reflux for 2 h and allowed to stir at room temperature
overnight. The suspension was poured onto ice, and the layers
were separated. The organic portion was washed with 10%
NaHCO3 and H2O and dried (MgSO4), and the solvent was
removed under vacuum to give 1.80 g (59%) of 15. The products
obtained by the two methods were identical by thin-layer
chromatography and NMR spectrometry. Compound 15 was
used in the preparation of 16 following the procedure described
for the synthesis of 13; aldehyde 16 was used without further
characterization in the synthesis of 4f (Table 1).
Meth od C. 2-Meth oxy-4-(5-p h en yl-1-p en tyn yl)ben za l-
d eh yd e (17). 5-Phenyl-1-pentyne (0.30 g, 2.00 mmol) was
added to a mixture of 10 (0.50 g, 1.76 mmol), CuI (0.01 g),
Et3N (5 mL), PdCl2 dppf (0.01 g, 0.08 mmol), and MeCN (10
mL) under N2 atmosphere and heated at reflux for 5 h. The
reaction mixture was cooled to room temperature, and the
solvent was removed under reduced pressure. The remaining
residue was extracted between EtOAc (4 × 50 mL) and H2O.
The organic layer was dried (MgSO4), and the solvent was
removed under reduced pressure to give an oil. The oil was
purified by flash chromatography (hexanes/EtOAc, 15:1) to
give 0.43 g (87%) of the title compound. 1H NMR (CDCl3) δ:
10.5 (s, 1H, CHO), 7.3 (d, 1H, ArH), 7.1-7.3 (m, 5H, ArH), 7.1
(m, 2H, ArH), 3.9 (s. 3H, OCH3), 2.8 (t, 2H, CH2), 2.4 (t, 2H,
CH2), 1.9 (m, 2H, CH2).
1
°C. H NMR (CDCl3) δ: 1.26 (d, 3H, CH3), 2.88 (d, 2H, CH2),
3.05 (t, 2H, CH2), 3.24 (t, 2H, CH2), 3.92 (s, 3H, OCH3), 4.15-
4.25 (m, 1H, CH), 6.92 (d, 1H, ArH), 7.20-7.33 (m, 5H, ArH),
7.76 (d, 1H, ArH), 7.89 (dd, 1H, ArH). The product was used
in the preparation of 6 without further characterization.
B. Molecu la r Mod elin g. The structures of 3d and 4i were
constructed from standard bond lengths and angles using the
SKETCH MOLECULE command in version 6.6 of SYBYL. The
structures were energy minimized with the Tripos force field,
and charges were calculated using the Gasteiger-Huckel
algorithm as implemented in SYBYL. A conformational search
was performed using the SYSTEMATIC SEARCH command;
rotatable bonds of the phenylpropyl tail were rotated in 30°
increments including the starting conformation. The results
were analyzed with the SEARCH routine of the SYBYL
program. The conformational searches identified >300 con-
formers with total energies ranging from 3.58 to 18.11 kcal/
mol and from 4.04 to 15.73 kcal/mol for 3d and 4i, respectively.
The lowest energy conformer in each series was further
energy minimized (3.58 and 3.45 kcal/mol, respectively), and
superimpositions were performed with the MULTIFIT com-
mand using the two aromatic centroids and terminal amine
of each compound. The energies were recalculated for each of
the individual conformers of the superimposed structure.
The same process was used to construct the structure of SR
46439B and to search for the lowest energy conformations
(allowing flexibility only for the rotatable bonds between the
two aromatic rings); 171 conformers were identified with
energies ranging from 10.16 to 38.12 kcal/mol. Further energy
minimization identified a conformer with an energy of 9.79
kcal/mol. MULTIFIT was used to compare this conformer with
the lowest energy conformers of 3d and 4i.
C. Ra d ioliga n d Bin d in g Assa ys. The binding assays were
conducted according to published procedures.7 Briefly, NIH-
3T3 cells stably transfected with rat 5-HT2A receptors (gener-
ously donated by Dr. David J ulius) and A-9 cells stably
transfected with rat 5-HT2C receptors (generously donated by
Dr. Beth Hoffman) were grown to confluence, suspended in
50 mM TRIS-HCl and centrifuged at 12,000 × g for 30 min.
The pellet was resuspended in buffer and centrifuged for an
additional 20 min. Assay buffer used in the experiments
consisted of 50 mM TRIS-HCl, 0.5 mM EDTA, 10 mM MgCl2,
and 0.1% ascorbate (pH 7.4). After resuspension in assay
buffer, 1 mL membrane aliquots (∼10 µg of protein measured
by bicinchoninic assay) were added to each tube containing 1
(()N-Tr iflu or oa cet yl-1-(2-m et h oxyp h en yl)-2-a m in o-
p r op a n e (19). Trifluoroacetic anhydride (1.15 mL, 8.16 mmol)
was added all at once to a solution of 1-(2-methoxy-phenyl)-
2-aminopropane (18) (1.30 g, 7.86 mmol) in dry benzene (10
mL). The reaction mixture was heated at reflux for 2 h, then
was allowed to cool to room temperature. The solvents were
removed under reduced pressure, and the residue was ex-
tracted between Et2O and 15% NaOH. The ethereal portion
was dried (MgSO4) and evaporated under reduced pressure
to give a white solid. Recrystallization from absolute EtOH/
H2O gave 1.38 g (67%) of the desired compound: mp 71-73
mL of assay buffer with either 0.5 nM [3H]ketanserin (5-HT2A
or 2.0 nM [3H]mesulergine (5-HT2C) and competing test agent.
Ketanserin (10 µM, 5-HT2A) and mesulergine (1 µM, 5-HT2C
)
)
were used to determine nonspecific binding. Competition
experiments were performed in triplicate in a 2.0 mL volume.
Membranes were incubated for 30 min at 37 °C, then filtered
on Schleicher and Schuell (Keene, NH) glass fiber filters
(presoaked in 0.1% polyethyleneimine), and washed with 10
mL of buffer. The filters were counted in an Ecoscint liquid
scintillation counter at 40% efficiency. Competition experi-
ments were plotted and analyzed using Graphpad Prism. Ki
1
°C. H NMR (CDCl3) δ: 1.26 (d, 3H, CH3), 2.86 (d, 2H, CH2),
3.86 (s, 3H, OCH3), 4.12-4.16 (m, 1H, CH), 6.89-6.96 (m, 2H,
ArH), 7.12 (dd, 1H, ArH), 7.26 (dt, 1H, ArH), 7.38 (bs, 1H, NH).
The product was used in the preparation of 20 without further
characterization.
values were determined from the Cheng-Prusoff equation20
:
Ki ) IC50/(1 + [D]/KD). The results reflect a minimum of three
(()N-Tr iflu or oa cetyl-1-[2-m eth oxy-5-(3-p h en yl-1-p r o-
p ion yl)p h en yl]-2-a m in op r op a n e (20). At -30 °C (dry ice/
acetone) and under a N2 atmosphere, titanium chloride (1.50
mL, 13.68 mmol) was added to a stirred solution of 19 (1.35 g,
5.17 mmol) in dry CH2Cl2 (25 mL), followed by the addition of
hydrocinnamoyl chloride (1.30 mL, 8.75 mmol) in dry CH2Cl2
(25 mL). The reaction mixture was allowed to warm to room
temperature where stirring continued under N2 for 3 d. The
reaction was quenched by pouring the mixture over ice/H2O
(10 g) and stirring for 15 min. The layers were separated. The
assays.
D. P I Hyd r olysis Assa y. Rat vascular smooth muscle cells
(A7r5; from ATCC, Rockville, MD) were maintained and
cultured by standard procedures as previously described.21 In
brief, the cells were grown in Dulbecco’s Modified Eagle
Medium (DMEM) containing 4.5 g/L glucose and 110 mg/L
sodium pyruvate, supplemented with 2 mM L-glutamine, 10
mg/mL gentamicin sulfate and 10% fetal bovine serum. The
cells were subcultured at 5-7-day intervals using 0.05%

1-[2-Methoxy-5-(3-phenylpropyl)]-2-aminopropane
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 20 3291
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trypsin/ 0.53 mM EDTA and were used within 10 passages
after thawing the frozen cells obtained form the vendor.
Previously published procedures were utilized to measure
[3H]inositol phosphates ([3H]-IPs) produced by agonist-activa-
tion of phospholipase C in the A7r5 cells.17,22 In brief, cells
grown to confluence in 24-well uncoated plastic plates were
exposed for 24-30 h to 1.0-1.5 mCi [3H]myoinositol (18.3 Ci/
mmol; Amersham Life Sciences Corp., Arlington Heights, IL)
in 0.5 mL of DMEM (serum-free, containing unlabeled myo-
inositol), corresponding to a specific activity of 37.5 mCi/mmol
[3H]myoinositol in the labeling medium. This permitted the
labeling of the cell membrane inositol lipid pool with [3H]-
myoinositol. Cells were then rinsed once with DMEM/F-12
containing 10 mM LiCl and then incubated with agonist in
the same medium for 1 h at 37 °C (triplicate determinations
for each concentration). Antagonist effects were determined
by adding the antagonist (or the solvent ethanol as a control23)
for 20 min prior to the 1 h incubation with agonist (serotonin;
5HT) After aspirating the medium, cells were lysed with 1 mL
of cold (4 °C) 0.1 M formic acid. The chromatographic separa-
tion of radiolabeled components on an AG- 1-X8 column was
performed exactly as previously described.21,22 The total [3H]-
IPs eluted with 4 mL of 1.2 M ammonium formate (containing
0.1 M formic acid) was mixed with 15 mL of Ecolume
scintillation fluid (ICN Biomedicals, Costa Mesa, CA) and
counted on a â-counter at ∼50% efficiency. RS-102221 (8-[5-
(2,4-dimethoxy-5-4-trifluoromethylphenylsulfonamido)phenyl-
5-oxopentyl]-1,3,8-triazaspiro[4.5]decane-2,4-dione hydrochlo-
ride), used as control, was purchased from Tocris Cookson (St.
Louis, MO).
5-Hydroxytryptamine2-family receptors (5-hydroxytryptamine2A
,
5-hydroxytryptamine2B, 5-hydroxytryptamine2C): Where struc-
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Gautret, B.; Neliat, G.; Labeeuw, B.; Le Fur, G.; Soubrie, P.;
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768.
E. Da ta An a lysis. The PI turnover functional data were
analyzed by the sigmoidal fit function of the Origin Scientific
Graphics software (Microcal Software, Northampton, MA) to
determine agonist potency (EC50) and intrinsic activity (IA)
values. The logistical equation employed for curve fitting was
A1 - A2
+ A2
1 + (x/x0)p
x0 ) EC50 or IC50; p ) power; A1 ) minimal Y value; A2
)
maximal Y value. The apparent intrinsic activity (IA) of the
agonists was defined relative to the maximal response to the
natural full agonist (5-HT) (IA set to 1.0 for full agonist; i.e.,
100% activity). Data from functional assays where various
antagonist concentrations were used against a single concen-
tration of 5-HT (10 µM) were analyzed using the equation of
Cheng-Prusoff.20 The Cheng-Prusoff equation is as follows:
Ki ) IC50/(1 + L/agonist EC50), where IC50 is the compound
concentration causing 50% inhibition of the functional re-
sponse, L is the agonist concentration used in the PI experi-
ments, and EC50 the potency of the agonist used (5-HT).
(16) Rinaldi-Carmona, M.; Congy, C.; Pointeau, P.; Vidal, H.; Breliere,
J . C.; Le Fur, G. Identification of binding sites for SR 46349B,
a 5-hydroxytryptamine2 receptor antagonist, in rodent brain. Life
Sci. 1993, 54, 119-127.
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silver sulphate. Tetrahedron Lett. 1993, 34, 6223-6244.
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A. Thyroid hormone analogues. Synthesis of 3′-substituted 3,5-
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50% inhibition (IC50) of an enzymatic reaction. Biochem. Phar-
macol. 1973, 22, 3099-3108.
Ack n ow led gm en t. This work was supported in part
by PHS Grant DA-01642 (R.A.G.) and MH 56650 (M.T.).
C.S.D. was the recipient of an AFPE Fellowship.
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