Exploring the structure-activity relationship of the ethylamine portion of 3-iodothyronamine for rat and mouse trace amine-associated receptor 1

Article abstract of DOI:10.1021/jm0700417

3-Iodothyronamine (1, T₁AM) is a naturally occurring derivative of thyroid hormone that can potently activate the orphan G protein-coupled receptor (GPCR) known as the trace amine-associated receptor 1 (TAAR ₁). We have previously found that modifying the outer ring of the phenoxyphenethylamine core scaffold of 1 can improve potency and provide potent agonists. In this study, we explored the tolerance of rat and mouse TAAR ₁ (rTAAR₁ and mTAAR₁) for structural modifications in the ethylamine portion of 1. We found that incorporating unsaturated hydrocarbon substituents and polar, hydrogen-bond-accepting groups were beneficial for rTAAR₁ and mTAAR₁, respectively, providing compounds that were equipotent or more potent than 1. Additionally, we have discovered that a naphthyl group is an excellent isosteric replacement for the iodophenyl ring of 1.

Full text of DOI:10.1021/jm0700417

J. Med. Chem. 2007, 50, 2787-2798
2787
Exploring the Structure-Activity Relationship of the Ethylamine Portion of 3-Iodothyronamine
for Rat and Mouse Trace Amine-Associated Receptor 1
Edwin S. Tan,† Motonori Miyakawa,‡ James R. Bunzow,§ David K. Grandy,§ and Thomas S. Scanlan*,‡
Chemistry and Chemical Biology Graduate Program and Departments of Pharmaceutical Chemistry and Cellular & Molecular Pharmacology,
UniVersity of California at San Francisco, 600 16th Street, San Francisco, California 94143-2280, and Department of Physiology and
Pharmacology, Oregon Health and Science UniVersity, 3181 Southwest Sam Jackson Park Road, Mail Code L334, Portland, Oregon 97239
ReceiVed January 12, 2007
3-Iodothyronamine (1, T1AM) is a naturally occurring derivative of thyroid hormone that can potently activate
the orphan G protein-coupled receptor (GPCR) known as the trace amine-associated receptor 1 (TAAR1).
We have previously found that modifying the outer ring of the phenoxyphenethylamine core scaffold of 1
can improve potency and provide potent agonists. In this study, we explored the tolerance of rat and mouse
TAAR1 (rTAAR1 and mTAAR1) for structural modifications in the ethylamine portion of 1. We found that
incorporating unsaturated hydrocarbon substituents and polar, hydrogen-bond-accepting groups were beneficial
for rTAAR1 and mTAAR1, respectively, providing compounds that were equipotent or more potent than 1.
Additionally, we have discovered that a naphthyl group is an excellent isosteric replacement for the iodophenyl
ring of 1.
Introduction
3-Iodothyronamine (1, T1AM;a Figure 1), a decarboxylated
and deiodinated metabolite of thyroxine (T4; Figure 1) and
3,3′,5-triiodothyronine (T3; Figure 1), is an endogenous com-
pound that can potently activate the orphan G protein-coupled
receptor (GPCR) known as the trace amine associated receptor
1 (TAAR1).1,4,5 Compound 1 activates rat and mouse TAAR1
(rTAAR1 and mTAAR1) with effective concentrations for half-
maximal stimulation (EC50) of 14 nM and 112 nM, respectively.
Initial pharmacological studies by Bunzow et al.3 showed that
rat TAAR1 can tolerate a diverse set of structural moieties in
the alkylamine portion of the ligands. It can be maximally
activated by compounds having simple ethylamine groups (i.e.,
Figure 1. Structures of thyroxine (T4), 3,3′,5-triiodothyronine (T3),
3-iodothyronamine (1, T1AM), and phenyltyramine (2, PTA).
tyramine, phenethylamine, 4-hydroxyamphetamine) or complex,
rigid, and/or highly functionalized alkylamines [i.e., dihydro-
ergotamine, agroclavine, R-(-)-apomorphine].
Results
Previously we have demonstrated that rTAAR1 and mTAAR1
can tolerate different alkylation states at the charged amine and
changes in both the outer and inner rings of the phenoxyphen-
Synthesis. Since rTAAR1 and mTAAR1 are homologous to
the â-adrenergic (âAR) and dopamine receptors, we explored
their tolerance for structural features commonly found in existing
âAR and dopamine receptor agonists and antagonists. These
structural motifs were incorporated into phenyltyramine (2, PTA;
Figure 1) rather than 1 because omitting the outer-ring hydroxyl
and inner-ring iodine significantly simplified the syntheses.
The aryloxypropylamines (Scheme 1) contain an oxymeth-
ylene bridge between the aromatic and ethylamine groups as
found in the â blockers alprenolol, pindolol, and propranolol
(Figure 2). Compounds 3 (ET-1) and 5 (ET-11) were readily
synthesized by coupling Boc-3-bromopropylamine (29) with p-
and m-phenoxyphenol to provide ethers 32 and 33, respectively.
Boc deprotection with 3 N anhydrous HCl gave the hydrochlo-
ride salts of 3 and 5 in good yields. Mono-N-methyl 6 (ET-12)
was obtained by reacting 32 with NaH and MeI followed by
acid deprotection. Di-N-methyl 4 (ET-6) was synthesized by
Eschweiler-Clarke reaction of the free amine of 3.6
ethylamine core scaffold of 1.2 3-Iodophenyltyramine (EC50
)
2.4 nM) and N-methyl-4′-fluoro-3-iodofluorophenyltyramine
(EC50 ) 2.7 nM) were found to be the most potent compounds
for rTAAR1 and N-methyl-p-trifluorobenzyltyramine (EC50
)
12 nM) for mTAAR1. In this study, we explore the structure-
activity relationship (SAR) of the ethylamine portion and expand
the SAR of the phenoxyphenethylamine core of 1. Here we
report four distinct scaffolds that are equipotent or more potent
than 1.
* To whom correspondence should be addressed: phone (503) 494-9292;
fax (503) 494-9275; e-mail scanlant@ohsu.edu.
† Chemistry and Chemical Biology Graduate Program, UCSF.
‡ Departments of Pharmaceutical Chemistry and Cellular & Molecular
Pharmacology, UCSF.
§ Oregon Health and Science University.
a Abbreviations: T1AM, 3-iodothyronamine; TAAR1, trace amine-
associated receptor 1; rTAAR1, rat trace amine-associated receptor 1;
mTAAR1, mouse trace amine-associated receptor 1; hTAAR1, human trace
amine-associated receptor 1; SAR, structure-activity relationship; GPCR,
G protein-coupled receptor; âAR, â-adrenergic receptor; PTA, phenyl-
tyramine; HEK293, human embryonic kidney 293; cAMP, cyclic adenosine
monophosphate; EFC, enzyme fragment complementation.
The benzamidoalkylamines (Scheme 2) contained an amide
linker between the aromatic and ethylamine portion of the
phenoxyphenethylamine scaffold, similar to dopamine receptor
antagonists metoclopramide, nafadotride, and sulpiride (Figure
2). The length of the carbon chain connecting the basic and
10.1021/jm0700417 CCC: $37.00 © 2007 American Chemical Society
Published on Web 05/12/2007

2788 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12
Tan et al.
Figure 2. Structures of â-adrenergic receptor (alprenolol, pindolol, and propranolol) and dopamine receptor (metoclopramide, nafadotride, sulpiride,
SKF 38393, and SCH 23390) ligands used as models for TAAR1 ligand design.
Scheme 1. Synthesis of Aryloxypropylaminesa
a Reagents and conditions: (a) Boc2O, NaHCO3, THF/H2O, 78%. (b) (i) NaH, DMF, 0 °C; (ii) 29, DMF, 83-91%. (c) 3 N HCl (anhydrous in EtOAc),
53-75%. (d) (i) NaH, DMF, 0 °C. (ii) MeI, 62%. (e) 3 N HCl (anhydrous in EtOAc), 90%. (f) (i) K2CO3, H2O; (ii) H2CO, HCO2H, 80 °C; (iii) 3 N HCl
(anhydrous in EtOAc), 76%.
amide nitrogen was varied from two to five carbons. Reaction
of the acyl chloride of 4-phenoxybenzoic acid and previously
reported monoprotected alkyldiamines 36-397 provided amides
40-43. Boc deprotection yielded the hydrochloride salts of
7-10 (ET-2 to ET-5) in poor to excellent yields. Dimethylated
11-14 (ET-7 to ET-10) were synthesized through an Esch-
weiler-Clarke reaction.
The â-phenylphenoxyphenethylamines (Scheme 3) and tet-
rahydrobenzazepines (Scheme 4) were modeled after the
prototypical dopamine receptor ligands SKF 38393 and SCH
23390 (Figure 2). Compounds 15 (ET-13) and 16 (ET-14) have
a â-phenyl ring alone, while 17 (ET-17) and 18 (ET-20) possess
a seven-membered ring in addition to the â-phenyl ring. The
reaction of the organolithium species of 4-bromodiphenyl ether
(44) with benzaldehyde and phenyl lithium with 3-phenoxy-
benzaldehyde (45) gave the dibenzylic alcohols 46 and 47,
respectively (Scheme 3). Initial attempts at converting this
alcohol into a nitrile group by nucleophilic displacement of the
corresponding mesylate with sodium cyanide were unsuccessful
due to the sterically congested nature of the dibenzylic alcohol.
Generating the chloride followed by reaction with TiCl4 and
trimethylsilylcyanide (TMSCN) successfully provided nitriles
48 and 49.8 Nitrile reduction with lithium aluminum hydride
and treatment with acid yielded the hydrochloride salts 15 and
16 in poor to modest yield.
Tetrahydrobenzazepines 53 and 55 were synthesized follow-
ing the published procedure for known compounds 52 and 54
(Scheme 4).9 Reacting 3-methoxyphenethylamine (50) with neat

SAR of the Ethylamine Portion of 3-Iodothyronamine
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12 2789
Scheme 2. Synthesis of Benzamidoalkylaminesa
a Reagents and conditions: (a) (i) SOCl2, DCM, DMF, reflux; (ii) 36-39, pyridine, DCM, 65-90%. (b) 3 N HCl (anhydrous in EtOAc), 96-100%. (c)
(i) K2CO3, H2O; (ii) H2CO, HCO2H, 80 °C; (iii) 3 N HCl (anhydrous in EtOAc), 11-98%.
Scheme 3. Synthesis of â-Phenylphenoxyphenethylaminesa
and subsequently reacted with Boc anhydride to provide Boc-
protected amines 66-68. Silyl deprotection with TBAF followed
by copper(II)-mediated biaryl ether formation with phenylbo-
ronic acid yielded 72-74. Acid deprotection resulted in biaryl
ether hydrochloride salts 19 (MM-7), 20 (MM-10), and 21 (MM-
13) in excellent yields.
Compounds 22 (MM-14) and 23 (MM-15) were both
synthesized from commercially available 4-phenoxybenzalde-
hyde (75). Piperidine-catalyzed condensation reaction with
Meldrum’s acid provided intermediate 76. Michael addition of
phenylacetylide and trimethylsilyl acetylide gave 77 and 78,
respectively, in good yields.12 Acetal deprotection and thermal
decarboxylation yielded acids 79 and 80. Base-mediated depro-
tection of 80 gave terminal alkyne 81. Curtius rearrangement
followed by acid exposure resulted in hydrochloride salts 22
and 23 in low yields.
Previously, we found that having a methyl group rather than
an iodine group at the 3-position of 1 was well tolerated in both
rTAAR1 and mTAAR1.2 Compared to 1, the potency of
3-methylthyronamine was only 2-fold lower in rTAAR1 and
essentially unaffected in mTAAR1. The phenoxynaphethy-
lamines (Scheme 6) were developed as another halogen-free
derivative to further probe the binding pocket occupied by the
iodine group of 1. Copper(II)-mediated coupling of 4-hydrox-
ynaphthadehyde (82) with phenylboronic acid provided
biaryl ether aldehyde 83. Following NaBH4 reduction, the
resulting alcohol was converted into a nitrile by treatment
with thionyl chloride followed by reaction with TiCl4 and
TMSCN. Nitrile 85 was then reduced with LiAlH4 and exposed
to acid to generate hydrochloride salt 24 (ET-21) in modest
yield.
A phenyl group was incorporated into the â-carbon of the
naphethylamine scaffold to determine if adding a phenyl ring
would enhance the potency of the naphethylamine scaffold as
observed with 15 and 16. Reaction of commercially available
4-methoxynaphthaldehyde (86) with phenylmagnesium bromide
quantitatively provided dibenzylic alcohol 87. Treatment with
thionyl chloride followed by TiCl4 and TMSCN provided nitrile
88. Nitrile reduction with LiAlH4 and exposure to acid gave
the primary amine hydrochloride salt 26 (ET-32). Methyl ether
deprotection with BBr3 and acid treatment precipitated naphthol
25 (ET-31). The Boc-protected amine 89 was subjected to
a Reagents and conditions: (a) (i) nBuLi, THF, -78 °C; (ii) benzalde-
hyde, 97%. (b) PhLi, THF, -78 °C, 86%. (c) (i) SOCl2, DCM; (ii) TMSCN,
TiCl4, DCM, 90-98%. (d) (i) LiAlH4, THF, reflux; (ii) 3 N HCl (anhydrous
in EtOAc), 26-47%.
styrene oxide gave benzylic alcohol 51. Treatment with trif-
luoroacetic acid in the presence of catalytic amounts of sulfuric
acid induced cyclization to form 53. Compound 53 was obtained
as an inseparable mixture with an unknown product. Methyl
ether deprotection with boron tribromide followed by acid
exposure gave pure hydrochloride salts of 55. Boc protection
of 54 and 55 followed by copper(II)-mediated coupling with
phenylboronic acid provided biaryl ethers 58 and 59.10 Boc
deprotection yielded 17 (ET-17) and 18 (ET-20) as hydrochlo-
ride salts.
To further explore the steric constraints around the â-carbon,
additional phenoxyphenethylamine derivatives possessing smaller
and bulkier substituents at the â-carbon were synthesized
(Scheme 5). Triisopropyl- (62) or tert-butyldimethylsilyl- (61)
protected 4-hydroxybenzylnitrile was treated with lithium di-
isopropylamine and methyl iodide or benzyl bromide to give
11
63, 64, or 65. The nitrile was reduced with LiAlH4-AlCl3

2790 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12
Scheme 4. Synthesis of Tetrahydrobenzazepinesa
Tan et al.
a Reagents and conditions: (a) styrene oxide, reflux, 36%. (b) TFA, H2SO4, reflux. (c) (i) BBr3, DCM; (ii) 3 N HCl (anhydrous in EtOAc), 40%. (d)
Boc2O, NaHCO3, THF/H2O, 61-81%. (e) PhB(OH)2, Cu(OAc)2, iPr2EtN, pyridine, 4 Å molecular sieves, DCM, 94-100%. (f) 3 N HCl (anhydrous in
EtOAc), 85-90%.
Table 1. Activity of 1 and 2 on rTAAR1 and mTAAR1
rTAAR1
Emaxb ( SEM (%)
mTAAR1
Emaxb ( SEM (%)
compd
R1
R2
EC50a ( SEM (nM)
Nc
EC50a ( SEM (nM)
Nc
1
2
OH
H
I
H
33 ( 3
63 ( 7
100 ( 0
93 ( 4
5
3
314 ( 43
420 ( 66
100 ( 0
85 ( 4
5
3
a Values represent the average of N independent experiments in triplicate and were calculated by use of Prism software as described in the Materials and
b
Methods section. Emax is the maximum stimulation achieved at a concentration of 10 µM and was calculated by use of Prism software. Emax ) 100% is
defined as the activity of compound 1 at 10 µM. c N is the number of independent experiments in triplicate that were performed and used to calculate the
EC50 and Emax values.
Table 2. Activity of Aryloxypropylamines 3-6 on rTAAR1 and mTAAR1
rTAAR1
Emaxb ( SEM (%)
mTAAR1
Emaxb ( SEM (%)
compd
R1
R2
R3
R4
EC50a ( SEM (nM)
Nc
EC50a ( SEM (nM)
Nc
3
4
5
6
OPh
OPh
H
H
H
OPh
H
H
CH3
H
H
CH3
H
758 ( 104
>1000
373 ( 9
370 ( 70
80 ( 3
36 ( 6
90 ( 7
46 ( 12
2
2
2
2
433 ( 154
464 ( 173
885 ( 549
66 ( 12
92 ( 2
62 ( 2
78 ( 13
113 ( 2
2
2
2
2
OPh
CH3
H
a-c See footnotes for Table 1.
copper(II)-mediated coupling to install the biaryl ether group
(90). Acid deprotection provided hydrochloride salt 27 (ET-
33) in good yield.
potency of compounds was consistent between the two assays.
Additionally, the EFC assay appears to have a better signal
range, providing the capacity to distinguish compounds that are
more efficacious than 1.
Inserting an oxymethylene bridge between the aromatic and
ethylamine portions of 2 had different effects on rTAAR1 and
mTAAR1 (Table 2). For rTAAR1, having an oxymethylene
bridge was detrimental. Compared to 2, the potency of 3
decreased ∼12-fold (EC50 ) 758 ( 104 nM, Emax ) 80% (
3%). Monomethylating the amine of 3 (6) improved the potency
Receptor Activation. As previously reported, both rTAAR1
and mTAAR1 are coupled to stimulatory G proteins and thus
induce cAMP production in HEK293 stable cell lines upon
agonist exposure.3,4 Representative dose-response curves of 1
in rTAAR1 and mTAAR1 are shown in Figure 3. It should be
noted that the measured EC50 values of 1 (Table 1) are
approximately 2- and 3-fold higher in rTAAR1 (EC50 ) 33 (
3 nM) and mTAAR1 (EC50 ) 314 ( 43 nM), respectively,
compared to previously reported values due to a change in assay
from a radioactive cAMP format to an enzyme fragment
complementation (EFC) format.13,14 However, the rank order
∼2-fold but decreased efficacy (EC50 ) 370 ( 70 nM, Emax
)
46% ( 12%). Dimethylation of 3 decreased both potency and
efficacy (EC50 > 1 µM, Emax ) 36% ( 6%). This trend was
consistent with previous SAR for rTAAR1, suggesting that

SAR of the Ethylamine Portion of 3-Iodothyronamine
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12 2791
Scheme 5. Synthesis of â-Substituted Phenoxyphenethylaminesa
a Reagents and conditions: (a) TBSCl or TIPSCl, imidazole, THF, 0 °C, 84-98%. (b) LDA, MeI or BnBr, -78 °C to rt, 75-98%. (c) (i) LiAlH4, AlCl3,
THF; (ii) Boc2O, NaHCO3, THF/H2O, 46-86%. (d) TBAF, THF, 0 °C, 91-96%. (e) PhB(OH)2, Cu(OAc)2, iPr2EtN, pyridine, 4 Å molecular sieves, DCM,
37-46%. (f) 3 N HCl (anhydrous in EtOAc), 92-94%. (g) Meldrum’s acid, piperidine, benzene, reflux, 70%. (h) PhCCLi or TMSCCH and nBuLi, THF,
-78 °C, 76-77%. (i) (i) 3 N HCl (anhydrous in EtOAc); (ii) dimethyl acetamide, 135 °C, 73-98%. (j) NaOH, MeOH, 76%. (k) (i) ClCO2Et, NaN3, Et3N,
acetone; (ii) toluene, reflux; (iii) 3 N HCl (anhydrous in EtOAc), 36-38%.
monomethylation of the amine can enhance potency and is
preferred over dimethylation.2 Interestingly, moving the phenoxy
group of 3 from the para to the meta position (5) increased
potency ∼2-fold and efficacy ∼10% (EC50 ) 373 ( 9 nM,
Emax ) 90% ( 7%).
For mTAAR1, the oxymethylene bridge was well tolerated
(Table 2). Compound 3 (EC50 ) 433 ( 154 nM, Emax ) 92%
( 2%) was just as potent and efficacious as 2. Monomethylation
of the amine (6) was very beneficial, enhancing the potency
∼6.5-fold and increasing efficacy by ∼21% (EC50 ) 66 ( 12
nM, Emax ) 113% ( 2%). Compound 6 was also more potent
than 1 by ∼4-fold. Dimethylated 4 activated mTAAR1 with
same potency as 3 but had a lower efficacy (EC50 ) 464 (
173 nM, Emax ) 62% ( 2%). This is also consistent with our
previous results showing that mTAAR1 can better accommodate
a dimethylamine moiety compared to rTAAR1.2 The decrease
in efficacy without a concomitant reduction in potency observed
by dimethylating the amine of 3 (4) suggests that it may be
possible to convert mTAAR1 agonists into antagonists by simply
adjusting the alkylation state of the amine. This may also apply
to rTAAR1, as monomethylation of 3 (6) decreased the efficacy
but improved potency. Contrary to rTAAR1, having the phenoxy
group at the meta position appears to be detrimental for
mTAAR1 since the potency and efficacy of 5 decreased ∼2-
fold and ∼14% (EC50 ) 885 ( 549 nM, Emax ) 78% ( 13%),
respectively, compared to 3.
In general, compounds based on the benzamidoalkylamine
scaffold were poor agonists for rTAAR1 (Table 3). All primary
and secondary amine derivatives (7-14) activated rTAAR1 with
EC50 values greater than 1 µM and efficacies equal to or less
than 69%. These benzamidoalkylamine analogues were also
poor agonists for mTAAR1 except for 14. Compound 14 was
∼4- and ∼3-fold more potent (EC50 ) 109 ( 6 nM) for
mTAAR1 compared to 2 and 1, respectively. The efficacy of

2792 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12
Tan et al.
Table 3. Activity of Benzamidoalkylamines 7-14 on rTAAR1 and mTAAR1
rTAAR1
mTAAR1
Emaxb ( SEM (%)
compd
n
R1
R2
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
EC50a ( SEM (nM)
Nc
7
8
9
10
11
12
13
14
2
3
4
5
2
3
4
5
H
H
H
H
CH3
CH3
CH3
CH3
H
H
H
H
CH3
CH3
CH3
CH3
>1000
>1000
>1000
>1000
>1000
>1000
>1000
>1000
4 ( 2
2 ( 1
2
2
2
2
2
2
2
2
>1000
>1000
17 ( 5
2 ( 1
1 ( 1
96 ( 5
7 ( 2
0 ( 2
3 ( 1
82 ( 4
2
2
2
2
2
2
2
3
31 ( 2
69 ( 7
5 ( 4
>1000
905 ( 261
>1000
2 ( 4
>1000
1 ( 4
>1000
44 ( 8
109 ( 6
a-c See footnotes for Table 1.
Scheme 6. Synthesis of â-Substituted Naphethylaminesa
a Reagents and conditions: (a) PhB(OH)2, Cu(OAc)2, iPr2EtN, pyridine, 4 Å molecular sieves, DCM, 39%. (b) NaBH4, EtOH, 95%. (c) (i) SOCl2, DCM;
(ii) TMSCN, TiCl4, DCM, 54%. (d) (i) LiAlH4, THF, reflux; (ii) 3 N HCl (anhydrous in EtOAc), 54%. (e) PhMgBr, THF, ∼100%. (f) (i) SOCl2, DCM; (ii)
TMSCN, TiCl4, DCM, 97%. (g) (i) LiAlH4, THF, reflux; (ii) 3 N HCl (anhydrous in EtOAc), 31%. (h) (i) BBr3, DCM; (ii) 3 N HCl (anhydrous in EtOAc),
72%. (i) Boc2O, NaHCO3, THF/H2O, 61%. (j) PhB(OH)2, Cu(OAc)2, iPr2EtN, pyridine, 4 Å molecular sieves, DCM, 55%. (k) 3 N HCl (anhydrous in
EtOAc), 84%.
14 (Emax ) 82% ( 4%) was comparable to that of 2.
Compounds with maximum efficacy less than 20% were not
antagonists for rTAAR1 or mTAAR1 as determined in competi-
tion assays measuring their ability to inhibit compound 1-in-
duced cAMP production (data not shown).
Appending a phenyl ring from the â-carbon of 2 was preferred
by rTAAR1 but not mTAAR1 (Table 4). The potency of 15
(EC50 ) 28 ( 2 nM, Emax ) 103% ( 4%) for rTAAR1 was
equivalent to that of 1 and ∼2-fold more potent than 2. Moving
the phenoxy group to the meta position (16) further increased
potency (EC50 ) 19 ( 2 nM) and efficacy (Emax ) 131% (
7%). For mTAAR1, the â-carbon phenyl substituent was
unfavorable, giving compounds with potencies greater than 1
µM and efficacies equal to or less than 35% for both compounds.
Compounds 15 and 16, as well as other compounds with
stereogenic centers (17, 18, 20-23, and 25-27), were evaluated
as racemic mixtures.
Cyclizing the amine to conformationally restrict the â-carbon
phenyl group gave tetrahydrobenzazepines (17 and 18) that were
equally weak agonists for both rTAAR1 and mTAAR1 (Table

SAR of the Ethylamine Portion of 3-Iodothyronamine
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12 2793
g 1 µM) and had lower efficacies (Emax e 72%). It should be
noted that 22 displayed some level of antagonist activity in
competition assays with 1, decreasing cAMP induction of 1 at
mTAAR1 ∼30% at a dose of 10 µM (data not shown).
Converting the inner ring of 2 from benzene to naphthalene
increased the potency and efficacy for both rTAAR1 and
mTAAR1 (Table 7). Compound 24 was ∼2-fold more potent
(EC50 ) 26 ( 1 nM) and ∼20% more efficacious (Emax ) 113%
( 5%) than 2. For mTAAR1, 24 was ∼20% more efficacious
and ∼4-fold more potent (EC50 ) 100 ( 22 nM) than 2. A
phenyl ring at the â-carbon (27) decreased the potency of 24
for rTAAR1 ∼2-fold. Compound 27 activated rTAAR1 with a
potency of 52 ( 4 nM and an efficacy of 100% ( 5%. Changing
the phenoxy group of 27 to a methoxy (26) or hydroxyl (25)
group decreased potency of 25 and 26 ∼5-14-fold (EC50
)
716 ( 269 nM and 270 ( 66 nM, respectively) and efficacy
∼10-30% (Emax ) 89% ( 3% and 71% ( 4%, respectively).
All the â-carbon phenyl derivatives of 24 (25-27) were at least
10-fold less potent at mTAAR1 (EC50 ) 1 µM) compared to 2.
When 25-27 were screened for antagonist activity in competi-
tion assays, only 27 displayed some degree of antagonism,
inhibiting compound 1-induced cAMP production at mTAAR1
∼50% at a dose of 10 µM (data not shown). The observed
activity of all compounds (3-27) tested were found to be
TAAR1-dependent, as all compounds showed no cAMP
accumulation when screened in an empty vector cell line (data
not shown).
Discussion
We have previously shown that the potency of 1 for both rat
and mouse TAAR1 can be improved by changing the methy-
lation state of the amine and/or modifying the outer-ring portion
of the phenoxyphenethylamine core scaffold.2 The pharmaco-
logical survey by Bunzow et al.3 showed that rTAAR1 could
be activated by phenethylamine analogues, amphetamines,
ergolines, and aminergic GPCR (dopamine, adrenergic, and
serotonin receptors) drugs with a structurally diverse range of
ethylamine segments. In this study, we synthesized a number
of phenyltyramine derivatives with structural modifications in
the ethylamine section to explore the SAR and determine if
structural variations in this region would lead to agonists for
rat and mouse TAAR1 that were more potent than 1.
Figure 3. Representative dose-response curves of potent agonists for
(a) rTAAR1 and (b) mTAAR1 stably expressed in HEK293 cells. (a)
Dose-response curves of 1 (9), 2 (0), 16 (B), and 24 (O) for rTAAR1.
(b) Dose-response curves of 1 (9), 2 (0), 6 (B), and 24 (O) for
mTAAR1. Data reported were normalized to 1 and expressed as a
percentage of compound 1 activity (% T1AM). Dose-response curves
were plotted and EC50 values were calculated with Prism software as
described in the Materials and Methods section.
The TAAR1 activity data showed that rat and mouse TAAR1
can tolerate prominent structural features commonly found in
the alkylamine fragment of existing âAR and dopamine receptor
agonists and antagonists; however, distinct TAAR1 species
preferences are evident. Extending the distance between the
charged amine and the aromatic ring of 2 by inserting an
oxymethylene bridge or an amide linker was tolerated by
mTAAR1 but not rTAAR1. On the other hand, appending a
phenyl ring at the â-carbon of 2 was detrimental for mTAAR1
activation but beneficial for rTAAR1 activation. The preference
for hydrocarbon functional groups with some degree of unsat-
uration at the â-carbon indicates that the binding pocket of
rTAAR1 around this position is primarily hydrophobic in nature.
Conversely, the tolerance for ether and amide groups in the
ethylamine chain of 2 suggests a more polar binding pocket in
the same region of mTAAR1.
5). The potencies of 17 and 18 were greater than 1 µM and the
efficacies did not surpass 86% for either receptor.
Increasing the size of the substituent at the â-carbon of 2 to
a benzyl (21) or phenylethynyl (23) was well tolerated by
rTAAR1 but not mTAAR1 (Table 6). Compound 21 was ∼2-
fold less potent (EC50 ) 140 ( 77 nM) but equally as
efficacious (Emax ) 92% ( 3%) as 2 for rTAAR1. Compound
23 was equipotent (EC50 ) 62 ( 15 nM) and more efficacious
(Emax ) 119% ( 3%) compared to 2. In mTAAR1, both 21
and 23 were weak agonists.
Smaller â-carbon substituents were also better tolerated in
rTAAR1 compared to mTAAR1 (Table 6). Adding one or two
methyl groups to the â-carbon of 2 decreased the potency for
rTAAR1 by 4-fold (EC50 ) 250 ( 132 nM and >1 µM for 20
and 19, respectively). Monomethyl 20 was comparably effica-
cious (Emax ) 94% ( 7%) to 2, whereas dimethyl 19 was
significantly less efficacious (Emax ) 13% ( 2%). Interestingly,
a small unsaturated acetylene group at the â-carbon (22) slightly
enhanced the potency (EC50 ) 41 ( 4 nM) without significantly
changing the efficacy (Emax ) 105% ( 14%) of 2 for rTAAR1.
For mTAAR1, all of these derivatives activated poorly (EC50
The two receptors also responded differently to changes in
the position of the phenoxy group. In general, the potency and
efficacy of compounds increased when the phenoxy group was
shifted from the para to the meta position in rTAAR1, as
observed with the change in activity from 3 to 5 and 15 to 16.
The same modification gives the opposite effect in mTAAR1,

2794 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12
Tan et al.
Table 4. Activity of â-Phenylphenoxyphenethylamines 15 and 16 on rTAAR1 and mTAAR1
rTAAR1
mTAAR1
Emaxb ( SEM (%)
compd
R1
R2
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
EC50a ( SEM (nM)
Nc
15
16
OPh
H
H
OPh
28 ( 2
19 ( 2
103 ( 4
131 ( 7
3
3
>1000
>1000
35 ( 8
15 ( 4
3
3
a-c See footnotes for Table 1.
Table 5. Activity of Tetrahydrobenzazepines 17 and 18 on rTAAR1 and mTAAR1
rTAAR1
mTAAR1
compd
R1
R2
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
17
18
Ph
H
H
Ph
>1000
>1000
32 ( 8
86 ( 2
2
2
>1000
>1000
22 ( 3
45 ( 5
2
2
a-c See footnotes for Table 1.
Table 6. Activity of â-Substituted Phenoxyphenethylamines 19-23 on rTAAR1 and mTAAR1
rTAAR1
mTAAR1
compd
R1
R2
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
19
20
21
22
23
CH3
CH3
Bn
CCH
CCPh
CH3
H
H
H
H
>1000
250 ( 132
140 ( 77
41 ( 4
13 ( 2
94 ( 7
2
2
2
3
3
>1000
>1000
18 ( 4
72 ( 7
31 ( 9
2 ( 5
2
2
2
2
2
92 ( 3
>1000
105 ( 14
119 ( 3
>1000
929 ( 314
62 ( 15
79 ( 9
a-c See footnotes for Table 1.
Table 7. Activity of Naphethylamines 24-27 on rTAAR1 and mTAAR1
rTAAR1
mTAAR1
compd
R1
R2
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
EC50a ( SEM (nM)
Emaxb ( SEM (%)
Nc
24
25
26
27
OPh
OH
OMe
OPh
H
26 ( 1
716 ( 269
270 ( 66
52 ( 4
113 ( 5
89 ( 3
71 ( 4
100 ( 6
3
2
2
3
101 ( 22
>1000
>1000
>1000
104 ( 3
14 ( 4
14 ( 4
0 ( 2
3
2
2
2
Ph
Ph
Ph
a-c See footnotes for Table 1.
leading to less potent and efficacious compounds. Confining
the ethylamine chain of 15 and 16 in a seven-membered ring
(17 and 18) to restrict the conformational orientations of the
â-carbon phenyl group was extremely detrimental to rTAAR1,
decreasing potency greater than 35-fold.
Transforming the phenethylamine ring of 2 into a naphthyl
ring was equally beneficial, improving the potency and efficacy
for rTAAR1 and mTAAR1 to the level of 1 or better. The
additional benzene ring in the naphthyl group of 24 most likely
occupies the iodine binding pocket in TAAR1 and is thus a good
isosteric replacement for the iodine present in 1. Contrary to
the phenoxyphenethylamine scaffold, appending a phenyl group
at the â-carbon of the phenoxynaphethylamine scaffold de-
creased the potency for rTAAR1. Having the bulkier
naphthyl group for an inner ring could possibly limit the
available torsional conformations of 27 and affect its ability

SAR of the Ethylamine Portion of 3-Iodothyronamine
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12 2795
volume). The cells were boiled for 20 min after addition of 100
µL of 0.5 mM sodium acetate buffer. The cell lysate was centrifuged
to remove cellular debris, and an aliquot (30 µL) was transferred
to an opaque, flat-bottom 96-well plate (Corning 3917). The
cAMP content of the aliquot was measured by use of the
Hithunter cAMP XS kit (DiscoveRX, Fremont, CA). The plate was
shaken on a titer plate shaker for 2 min after addition of 20 µL
of cAMP XS antibody/lysis mix. After incubation in the dark for
1 h, 20 µL of cAMP XS ED reagent was added and the plate
was shaken for 2 min. After another hour of incubation in the
dark, 40 µL of cAMP XS EA/CL substrate mix was added
and the plate was shaken for 2 min. The plate was allowed to
incubate in the dark for 18 h before luminescence was measured
(three readings/well at 0.33 s/reading) on an Analyst AD assay
detection system (LJL Biosystems) or a Packard Fusion microplate
reader. Data were reported relative to 1 and expressed as % T1-
AM. Concentration-response curves were plotted and EC50 values
were calculated with Prism software (GraphPad, San Diego, CA).
Standard error of the mean was calculated from the EC50 and Emax
values of each independent triplicate experiment by use of Prism
Software.
General Procedure for t-Boc Deprotection. The t-Boc-protected
amine (1.40 mmol) was dissolved in a 3 N anhydrous HCl solution
in ethyl acetate (3 mL), and the reaction mixture was stirred at
room temperature for 2-16 h. The reaction was exposed to diethyl
ether and the resulting amine hydrochloride salts were washed with
diethyl ether. If the amine hydrochloride salts did not form a
precipitate, the diethyl ether/ethyl acetate solution was concentrated
under reduced pressure and rinsed with diethyl ether to give the
hydrochloride salts.
General Procedure for N,N-Dimethylation of Amine Hydro-
chloride Salt. The amine hydrochloride salt (0.22 mmol) was
dissolved in water, treated with potassium carbonate (>0.22 mmol),
and extracted with dichloromethane. The organic layer was dried
over MgSO4, filtered, and concentrated under reduced pressure to
give the free amine. A solution of free amine (0.22 mmol), formic
acid (>1.10 mmol, 88% in water solution), and formaldehyde
(>1.10 mmol, 37% in water solution) was then stirred at 80 °C for
∼20 h. After cooling to room temperature, the reaction was diluted
with water, made basic (pH ∼10) with potassium carbonate, and
extracted with dichloromethane. The organic layer was washed with
brine, dried over MgSO4, and concentrated under reduced pressure
to give the crude product. The crude mixture was treated with a
solution of 3 N anhydrous HCl in ethyl acetate (1 mL) and exposed
to diethyl ether, and the resulting amine hydrochloride salts were
washed with diethyl ether. If the amine hydrochloride salts did not
form a precipitate, the diethyl ether/ethyl acetate solution was
concentrated under reduced pressure and rinsed with diethyl ether
to give the hydrochloride salt.
General Procedure for the Reduction of Nitrile to Amine
Hydrochloride. To a suspension of lithium aluminum hydride (26.7
mmol) in THF (56 mL) at 0 °C was added a solution of nitrile
(6.66 mmol) in THF (10 mL). After refluxing under argon for 24
h, the reaction was quenched with water (1.014 mL), 10% aqueous
sodium hydroxide (2.028 mL), and water (3.043 mL). The reaction
was filtered to remove the precipitated aluminum salts. The
filtrate was washed with water and brine and extracted with ethyl
acetate. The organic layer was dried over MgSO4, filtered, and
concentrated under reduced pressure to give the crude product. The
crude mixture was treated with a 3 N anhydrous HCl solution in
ethyl acetate (5-10 mL) and exposed to diethyl ether, and the
resulting amine hydrochloride salts were washed with diethyl ether.
If the amine hydrochloride salts did not form a precipitate, the
diethyl ether/ethyl acetate solution was concentrated under reduced
pressure and rinsed with diethyl ether to give the hydrochloride
salts.
to position the â-phenyl ring in the optimal orientation inside
the binding pocket of rTAAR1, resulting in decreased
potency. The considerable decrease in potency observed with
hydroxyl (25) or methoxy (26) substituents in place of the
phenoxy group illustrates the significant contribution of the
biaryl ether moiety to the potency of the phenoxynaphethylamine
scaffold.
The observed SAR preferences between the rat and mouse
TAAR1 were quite interesting, given that the two receptors are
93% similar. Since the rodent receptors are only 83-85%
similar to the human receptor, the SAR of the ethylamine portion
of 1 for the human TAAR1 (hTAAR1) may be different from
that of the rat or mouse TAAR1. Compound 1 has recently been
found to be significantly less potent for hTAAR1 by Wainscott
et al.15 when they investigated the pharmacological profile of
hTAAR1.
Conclusion
The present study demonstrates that it is possible to enhance
the potency of thyronamines for both rat and mouse TAAR1
by incorporating functionalities in the ethylamine portion of the
phenoxyphenethylamine scaffold. Rat and mouse TAAR1 have
different structural preferences in this region of the scaffold,
with rTAAR1 favoring unsaturated hydrocarbon groups and
mTAAR1 preferring functional groups that are polar and
hydrogen-bond acceptors. Despite this species variability,
transforming the inner ring of the phenoxyphenethylamine
scaffold into a naphthyl group was equally beneficial to both
receptors, mostly likely acting as an excellent isosteric replace-
ment for the iodophenyl inner ring of 1.
Materials and Methods
General. 1H and 13C NMR spectra were taken on a Varian 400
(400 and 100 MHz, respectively). Data reported are calibrated to
internal tetramethylsilane (TMS; 0.0 ppm) for all solvents unless
otherwise noted and are reported as follows: chemical shift,
multiplicity (app ) apparent, br ) broad, s ) singlet, d ) doublet,
t ) triplet, q ) quartet, m ) multiplet, dd ) doublet of doublet),
coupling constant, and integration. High-resolution mass spectrom-
etry (HRMS) with electrospray ionization was performed by the
Mass Spectrometry Laboratory, School of Chemical Sciences,
University of Illinois at Urbana-Champaign. Inert atmosphere
operations were conducted under argon passed through a drierite
drying tube in flame-dried or oven-dried glassware unless otherwise
noted. Anhydrous tetrahydrofuran (THF), dichloromethane (DCM),
diethyl ether, pyridine, and diisopropylethylamine were filtered
through two columns of activated basic alumina and transferred
under an atmosphere of argon gas in a solvent purification
system designed and manufactured by Seca Solvent Systems.
Anhydrous N,N-dimethylformamide (DMF) was obtained by pass-
ing through two columns of activated molecular sieves. All
other anhydrous solvents and reagents were purchased from
Aldrich, Sigma-Aldrich, Fluka, Alfa Aesar, or Acros and were
used without any further purification unless otherwise stated.
1
Final compounds were judged to be > 95% pure by H NMR
analysis and confirmed HPLC. HPLC was performed on an Agilent
1200 Series LC system [using a Waters XTerra Phenyl 3.5 µm
(3.0 × 50 mm) column] with a gradient of 0-90% acetonitrile
(0.1% TFA) over 8 min and 0-100% methanol (0.05% TFA) over
8 or 10 min.
In Vitro cAMP Assays. After incubation in fresh medium for
at least 2 h, HEK293 cells stably transfected with either rTAAR1
or mTAAR1 were harvested in Krebs-Ringer-HEPES buffer
(KRH) and preincubated with 200 µM 3-isobutyl-1-methylxanthine
(IBMX) for 20-30 min. Cells were incubated in KRH with 133
µM IBMX and 3 µL of the test compound, forskolin (10 µM), or
vehicle (dimethyl sulfoxide, DMSO) for 1 h at 37 °C (300 µL total
General Procedure for Curtius Rearrangement. To a solution
of acid (500 mg, 1.46 mmol), ethylchloroformate (0.16 mL, 1.61
mmol), and triethylamine (0.2 mL, 1.46 mmol) in acetone (10 mL)
at 0 °C was added a solution of sodium azide (210 mg, 3.21 mmol)
in water (2 mL). The reaction was stirred for 1 h and then diluted

2796 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12
Tan et al.
with ether. The reaction was washed with water and brine, dried
over MgSO4, and concentrated under reduced pressure. The
crude product was dissolved in toluene (20 mL) and refluxed
for 1 h. After cooling to ambient temperature, the crude
mixture was concentrated in vacuo. The crude product was
dissolved in dioxane (5 mL), concentrated HCl (3 mL), and water
(3 mL) and then refluxed for 1 h. After cooling to ambient
temperature, the crude mixture was diluted with ether, washed with
water and brine, dried over MgSO4, and concentrated under reduced
pressure.
(t, J ) 6.8 Hz, 2H), 2.93 (t, J ) 7.8 Hz, 2H), 1.69 (m, 4H), 1.46
(m, 2H). HRMS (EI+) m/ z for C18H22N2O2 [M + H]+: calcd,
299.1760; found, 299.1767.
N,N-Dimethyl-2-(4-phenoxybenzamido)ethylamine Hydro-
chloride (11). Refer to general procedure for N,N-dimethylation
fo amine hydrochloride salt described above: 0.09 g, 98% yield.
1H NMR (400 MHz, methanol-d4) δ 7.87 (d, J ) 8.8 Hz, 2H),
7.42(t, J ) 7.8 Hz, 2H), 7.21 (t, J ) 7.6 Hz, 1H), 7.05 (d, J ) 8.8
Hz, 2H), 7.02 (d, J ) 9.2 Hz, 2H), 3.74 (t, J ) 5.8 Hz, 2H), 3.37
(t, J ) 5.8 Hz, 2H), 2.98 (s, 6H). HRMS (EI+) m/z for C17H20N2O2
[M + H]+: calcd, 285.1603; found, 285.1609.
3-[(4-Phenoxyphenyl)oxy]propylamine Hydrochloride (3).
Refer to general procedure for t-Boc deprotection described
N,N-Dimethyl-3-(4-phenoxybenzamido)propylamine Hydro-
chloride (12). Refer to general procedure for N,N-dimethylation
fo amine hydrochloride salt described above: 0.12 g, 76%
1
above: 0.12 g, 53% yield). H NMR (400 MHz, methanol-d4) δ
7.29 (t, J ) 8.0 Hz, 2H), 7.04 (t, J ) 7.4 Hz, 1H), 6.96 (s, 4H),
6.89 (d, J ) 7.6 Hz, 2H), 4.11 (t, J ) 5.8 Hz, 2H), 3.16 (t, J ) 7.2
Hz, 2H), 2.14 (m, 2H). HRMS (EI+) m/z for C15H17NO2 [M +
H]+: calcd, 244.1338; found, 244.1343.
1
yield. H NMR (400 MHz, methanol-d4) δ 7.86 (d, J ) 8.8 Hz,
2H), 7.41 (t, J ) 8.1 Hz, 2H), 7.20 (t, J ) 7.6 Hz, 1H), 7.05
(d, J ) 7.8 Hz, 2H), 7.01 (d, J ) 8.8 Hz, 2H), 3.48 (t, J ) 6.6 Hz,
2H), 3.19 (t, J ) 7.6 Hz, 2H), 2.91 (s, 6H), 2.03 (m, 2H). HRMS
(EI+) m/z for C18H22N2O2 [M + H]+: calcd, 299.1760; found,
299.1757.
N,N-Dimethyl-3-[(4-phenoxyphenyl)oxy]propylamine Hydro-
chloride (4). Refer to general procedure for N,N-dimethylation to
1
amine hydrochloride salt described above; 0.17 g, 76% yield. H
NMR (400 MHz, methanol-d4) δ 7.30 (t, J ) 8.0 Hz, 2H), 7.04 (t,
J ) 7.4 Hz, 1H), 6.96 (s, 4H), 6.89 (d, J ) 8.0 Hz, 2H), 4.10 (d,
J ) 5.8 Hz, 2H), 3.32 (m, 2H), 2.92 (s, 6H), 2.21 (m, 2H). HRMS
(EI+) m/z for C17H21NO2 [M + H]+: calcd, 272.1651; found,
272.1641.
N,N-Dimethyl-4-(4-phenoxybenzamido)butylamine Hydro-
chloride (13). Refer to general procedure for N,N-dimethylation
to amine hydrochloride salt: 0.16 g, 11% yield. 1H NMR
(400 MHz, methanol-d4) δ 7.82 (d, J ) 8.8 Hz, 2H), 7.41 (t, J )
7.8 Hz, 2H), 7.20 (t, J ) 7.4 Hz, 1H), 7.06 (d, J ) 7.6 Hz, 2H),
7.00 (d, J ) 8.8 Hz, 2H), 3.43 (t, J ) 6.8 Hz, 2H), 3.19
(t, J ) 8.0 Hz, 2H), 2.89 (s, 6H), 1.77 (m, 2H), 1.69 (m, 2H).
HRMS (EI+) m/z for C19H24N2O2 [M + H]+: calcd, 313.1916;
found, 313.1925.
3-[(3-Phenoxyphenyl)oxy]propylamine Hydrochloride (5).
Refer to general procedure for t-Boc deprotection described
1
above: 0.76 g, 75% yield. H NMR (400 MHz, methanol-d4) δ
7.35 (t, J ) 8.2 Hz, 2H), 7.24 (t, J ) 8.4 Hz, 1H), 7.12 (t, J ) 7.4
Hz, 1H), 6.98 (d, J ) 7.6 Hz, 2H), 6.70 (app d, J ) 7.6 Hz, 1H),
6.57 (app s, 1H), 6.56 (app s, 1H), 4.08 (t, J ) 5.8 Hz, 2H), 3.13
(t, J ) 7.2 Hz, 2H), 2.12 (m, 2H). HRMS (EI+) m/z for C15H17-
NO2 [M + H]+: calcd, 244.1338; found, 244.1339.
N,N-Dimethyl-5-(4-phenoxybenzamido)pentylamine Hydro-
chloride (14). Refer to general procedure for N,N-dimethylation
1
fo amine hydrochloride salts: 0.09 g, 31% yield. H NMR (400
MHz, methanol-d4) δ 7.82 (d, J ) 8.8 Hz, 2H), 7.41 (t, J ) 8.0
Hz, 2H), 7.20 (t, J ) 7.6 Hz, 1H), 7.04 (d, J ) 8.4 Hz, 2H), 7.00
(d, J ) 8.8 Hz, 2H), 3.40 (t, J ) 6.0 Hz, 2H), 3.13 (t, J ) 7.8 Hz,
2H), 2.88 (s, 6H), 1.78 (m, 2H), 1.69 (m, 2H), 1.46 (m, 2H). HRMS
(EI+) m/z for C20H26N2O2 [M + H]+: calcd, 327.2073; found,
327.2087.
2-(4-Phenoxyphenyl)-2-phenylethylamine Hydrochloride (15).
Refer to general procedure for the reduction of nitrile to amine
hydrochloride described above: 0.24 g, 47% yield. 1H NMR (400
MHz, methanol-d4) δ 7.22-7.35 (m, 9H), 7.04 (t, J ) 7.6 Hz, 1H),
6.89-6.92 (m, 4H), 4.22 (t, J ) 8.0 Hz, 1H), 3.56 (d, J ) 8.0 Hz,
1H). HRMS (EI+) m/z for C20H19NO [M + H]+: calcd, 290.1545;
found, 290.1559.
2-(3-Phenoxyphenyl)-2-phenylethylamine Hydrochloride (16).
Refer to general procedure for the reduction of nitrile to amine
hydrochloride described above: 2.79 g, 26% yield. 1H NMR (400
MHz, methanol-d4) δ 7.34 (m, 10H), 7.12 (app t, J ) 7.3 Hz, 1H),
6.98 (m, 1H), 6.86 (dd, J ) 8.1, 2.7 Hz, 1H), 4.26 (t, J ) 8.1 Hz,
1H), 3.62 (d, J ) 8.3 Hz, 2H). HRMS (EI+) m/z for C20H19NO [M
+ H]+: calcd, 290.1545; found, 290.1548.
N-Methyl-3-[(4-phenoxyphenyl)oxy]propylamine Hydrochlo-
ride (6). Refer to general procedure for t-Boc deprotection
described above: 0.94 g, 90% yield. 1H NMR (400 MHz,
methanol-d4) δ 7.29 (t, J ) 8.0 Hz, 2H), 7.04 (t, J ) 7.4 Hz, 1H),
6.96 (s, 4H), 6.90 (app t, J ) 7.4 Hz, 2H), 4.11 (t, J ) 5.8 Hz,
2H), 3.23 (t, J ) 7.2 Hz, 2H), 2.74 (s, 3H), 2.17 (m, 2H). HRMS
(EI+) m/z for C16H18NO2 [M + H]+: calcd, 258.1494; found,
258.1503.
2-(4-Phenoxybenzamido)ethylamine Hydrochloride (7). Refer
to general procedure for t-Boc deprotection described above: 0.25
g, ∼100% yield. 1H NMR (400 MHz, methanol-d4) δ 7.88 (d, J )
8.8 Hz, 2H), 7.41(t, J ) 7.8 Hz, 2H), 7.20 (t, J ) 7.4 Hz, 1H),
7.05 (d, J ) 8.0 Hz, 2H), 7.01 (d, J ) 8.8 Hz, 2H), 3.66 (t, J ) 5.8
Hz, 2H), 3.17 (t, J ) 6.0 Hz, 2H); 13C NMR (400 MHz, methanol-
d4) δ 170.5, 162.5, 157.2, 131.2, 130.6, 129.1, 125.6, 121.0, 118.4,
41.4, 38.8. HRMS (EI+) m/z for C15H16N2O2 [M + H]+: calcd,
257.1290; found, 257.1293.
3-(4-Phenoxybenzamido)propylamine Hydrochloride (8). Re-
fer to general procedure for t-Boc deprotection described above:
0.23 g, 96% yield. 1H NMR (400 MHz, methanol-d4) δ 7.84 (d, J
) 8.8 Hz, 2H), 7.41 (t, J ) 8.1 Hz, 2H), 7.20 (t, J ) 7.3 Hz, 1H),
7.06 (d, J ) 7.8 Hz, 2H), 7.01 (d, J ) 8.8 Hz, 2H), 3.49 (t, J ) 6.6
Hz, 2H), 2.98 (t, J ) 7.3 Hz, 2H), 1.94 (quintet, J ) 7.0 Hz, 2H).
HRMS (EI+) m/z for C16H18N2O2 [M + H]+: calcd, 271.1447;
found, 271.1447.
8-Phenoxy-1-phenyl-2,3,4,5-tetrahydro-3-benzazepine Hy-
drochloride (17). Refer to general procedure for t-Boc depro-
1
tection described above: 0.50 g, 90% yield. H NMR (400 MHz,
methanol-d4) δ 7.40 (t, J ) 7.6 Hz, 2H), 7.32 (app t, J ) 7.4 Hz,
2H), 7.27 (m, 2H), 7.19 (d, J ) 7.6 Hz, 2H), 7.07 (t, J ) 7.4 Hz,
1H), 6.87 (d, J ) 7.6 Hz, 2H), 6.81 (dd, J ) 8.4, 2.4 Hz, 1H), 6.40
(d, J ) 1.6 Hz, 1H), 4.61 (d, J ) 8.4 Hz, 1H), 3.72 (m, 2H), 3.48
(dd, J ) 11.8, 7.6 Hz, 2H), 3.18 (m, 2H). HRMS (EI+) m/z for
C22H21NO [M + H]+: calcd, 316.1701; found, 316.1713.
4-(4-Phenoxybenzamido)butylamine Hydrochloride (9).
Refer to general procedure for t-Boc deprotection described
1
above: 0.21 g, 97% yield. H NMR (400 MHz, methanol-d4) δ
7.82 (d, J ) 9.3 Hz, 2H), 7.41 (t, J ) 8.1 Hz, 2H), 7.20 (t, J ) 7.3
Hz, 1H), 7.05 (d, J ) 8.8 Hz, 2H), 7.00 (d, J ) 8.8 Hz, 2H), 3.42
(t, J ) 6.6 Hz, 2H), 2.98 (t, J ) 7.1 Hz, 2H), 1.71 (m, 4H). HRMS
(EI+) m/z for C17H20N2O2 [M + H]+: calcd, 285.1603; found,
285.1603.
7-Phenoxy-1-phenyl-2,3,4,5-tetrahydro-3-benzazepine Hy-
drochloride (18). Refer to general procedure for t-Boc depro-
1
tection described above: 0.10 g, 85% yield. H NMR (400 MHz,
methanol-d4) δ 7.44 (t, J ) 7.6 Hz, 3H), 7.35 (app t, J ) 8.1 Hz,
3H), 7.23 (d, J ) 8.1, 2H), 7.12 (t, J ) 7.3 Hz, 1H), 7.00 (dd, J )
8.8, 1.0 Hz, 1H), 6.90 (s, 1H), 6.77 (s, 2H), 4.60 (dd, J ) 8.6, 1.7
Hz, 1H), 3.66-3.84 (m, 2H), 3.22 (m, 2H), 3.09 (m, 2H). HRMS
(EI+) m/z for C22H21NO [M + H]+: calcd, 316.1701; found,
316.1702.
5-(4-Phenoxybenzamido)pentylamine Hydrochloride (10).
Refer to general procedure for t-Boc deprotection described
1
above: 0.13 g, 98% yield. H NMR (400 MHz, methanol-d4) δ
7.81 (d, J ) 8.8 Hz, 2H), 7.41 (t, J ) 8.1 Hz, 2H), 7.20 (t, J ) 7.6
Hz, 1H), 7.05 (d, J ) 8.8 Hz, 2H), 7.00 (d, J ) 9.3 Hz, 2H), 3.39

SAR of the Ethylamine Portion of 3-Iodothyronamine
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12 2797
2-Methyl-2-(4-phenoxyphenyl)propan-1-amine Hydrochloride
(19). Refer to general procedure for t-Boc deprotection described
above: white solid, 46 mg, 92% yield. 1H NMR (400 MHz, DMSO-
d6) δ 7.72 (br s, 3H), 7.44-7.37 (m, 4H), 7.14 (t, J ) 7.6 Hz, 1H),
7.02-6.99 (m, 4H), 3.32 (s, 2H), 1.35 (s, 6H); 13C NMR (100 MHz,
methanol-d4) δ 158.45, 157.91, 139.98, 130.91, 128.65, 124.61,
119.99, 51.74, 38.03, 26.97. HRMS (EI+) m/z for C16H19NO [M
+ H]+: calcd, 241.1467; found, 241.1457.
g, 72%). 1H NMR (400 MHz, methanol-d4) δ 8.27 (d, J ) 8.4 Hz,
1H), 8.01 (d, J ) 9.0 Hz, 1H), 7.44 (m, 3H), 7.35 (m, 4H), 7.23
(m, 1H), 6.89 (d, J ) 7.9 Hz, 1H), 5.03 (t, J ) 8.0 Hz, 1H), 3.70
(m, 2H). HRMS (EI+) m/z for C18H17NO [M + H]+: calcd,
264.1388; found, 264.1388.
2-(1-Methoxynaphthalen-4-yl)-2-phenylethylamine Hydro-
chloride (26). Refer to general procedure for the reduction of nitrile
1
to amine hydrochloride described above: 0.26 g, 31% yield. H
2-(4-Phenoxyphenyl)propan-1-amine Hydrochloride (20). Re-
fer to general procedure for t-Boc deprotection described above:
white solid, 95 mg, 93% yield. 1H NMR (400 MHz, DMSO-d6) δ
7.82 (s, 2H), 7.40 (app t, J ) 8.2 Hz, 2H), 7.31 (d, J ) 7.0 Hz,
2H), 7.14 (app t, J ) 8.2 Hz, 1H), 7.00 (m, 4H), 3.02 (m, 1H),
1.26 (d, J ) 6.0 Hz, 3H); 13C NMR (100 MHz, methanol-d4) δ
158.59, 158.14, 137.99, 130.88, 129.71, 124.49, 120.33, 119.89,
46.88, 38.94, 19.99. HRMS (EI+) m/z for C15H17NO [M + H]+:
calcd, 227.1310; found, 227.1306.
NMR (400 MHz, methanol-d4) δ 8.28 (m, 1H), 8.04 (d, J ) 7.9
Hz, 1H), 7.47 (m, 3H), 7.35 (m, 4H), 7.24 (m, 1H), 6.97 (d, J )
8.1 Hz, 1H), 5.05 (t, J ) 8.0 Hz, 1H), 4.03 (s, 3H), 3.72 (m, 2H).
HRMS (EI+) m/z for C19H19NO [M + H]+: calcd, 278.1545; found,
278.1550.
2-(1-Phenoxynaphthalen-4-yl)-2-phenylethylamine Hydro-
chloride (27). Refer to general procedure for t-Boc deprotection
described above: slightly yellow solid, 0.058 g, 84% yield. 1H NMR
(400 MHz, methanol-d4) δ 8.24 (m, 1H), 8.16 (d, J ) 7.9 Hz, 1H),
7.56 (m, 1H), 7.50 (m, 2H), 7.37 (m, 6H), 7.25 (m, 1H), 7.14 (m,
1H), 7.04 (m, 2H), 6.95 (d, J ) 8.1 Hz, 1H), 5.13 (t, J ) 7.9 Hz,
1H), 3.74 (m, 2H). HRMS (EI+) m/z for C24H21NO [M + H]+:
calcd, 340.1701; found, 340.1716.
2-(4-Phenoxyphenyl)-3-phenylpropan-1-amine Hydrochloride
(21). Refer to general procedure for t-Boc deprotection
1
described above: white solid, 70 mg, 94% yield. H NMR (400
MHz, DMSO-d6) δ 7.79 (s, 2H), 7.38 (t, J ) 8.0 Hz, 2H), 7.25 (d,
J ) 8.6 Hz, 2H), 7.22 (d, J ) 7.5 Hz, 2H), 7.14 (m, 2H), 7.07 (d,
J ) 7.5 Hz, 2H), 6.95 (t, J ) 7.5 Hz, 4H), 3.29 (m, 1H), 3.11 (m,
3H), 2.82 (dd, J ) 8.6, 13.6 Hz, 1H); 13C NMR (100 MHz,
methanol-d4) δ 158.58, 158.23, 139.94, 135.54, 130.87, 130.64,
130.17, 129.37, 127.46, 124.49, 120.28, 119.84, 46.95, 45.01, 41.78.
HRMS (EI+) m/z for C21H21NO [M + H]+: calcd, 303.1623; found,
303.1621.
2-(4-Phenoxyphenyl)-4-phenylbut-3-yn-1-amine Hydrochlo-
ride (22). Refer to general procedure for Curtius rearrangement
described above. The crude product was purified via flash SiO2
chromatography [eluted with methanol/ethyl acetate (1:4)] to give
the pure product 22 as a white solid (185 mg, 36% yield). 1H NMR
(400 MHz, DMSO-d6) δ 8.19 (s, 4H), 7.53 (t, J ) 8.3 Hz, 4H),
7.41 (m, 5H), 7.16 (t, J ) 7.4 Hz, 1H), 7.05 (t, J ) 8.9 Hz, 4H),
4.36 (t, J ) 6.9 Hz, 1H), 3.21 (m, 2H); 13C NMR (100 MHz,
methanol-d4) δ 158.85, 158.29, 132.84, 130.95, 130.36, 129.76,
129.48, 124.74, 123.75, 120.17, 120.12, 86.95, 46.29, 37.23. HRMS
(EI+) m/z for C22H19NO [M + H]+: calcd, 313.1467; found,
313.1367.
Acknowledgment. This research was supported by a grant
from the National Institutes of Health (Grant DK52798 to
T.S.S.).
Supporting Information Available: Experimental procedures
for all intermediates and HPLC data for final compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
References
(1) Scanlan, T. S.; Suchland, K. L.; Hart, M. E.; Chiellini, G.; Huang,
Y.; Kruzich, P. J.; Frascarelli, S.; Crossley, D. A.; Bunzow, J. R.;
Ronca-Testoni, S.; Lin, E. T.; Hatton, D.; Zucchi, R.; Grandy, D. K.
3-Iodothyronamine is an endogenous and rapid-acting derivative of
thyroid hormone. Nat. Med. 2004, 10 (6), 638-42.
(2) Hart, M. E.; Suchland, K. L.; Miyakawa, M.; Bunzow, J. R.; Grandy,
D. K.; Scanlan, T. S. Trace amine-associated receptor agonists:
synthesis and evaluation of thyronamines and related analogues. J.
Med. Chem. 2006, 49 (3), 1101-12.
(3) Bunzow, J. R.; Sonders, M. S.; Arttamangkul, S.; Harrison, L. M.;
Zhang, G.; Quigley, D. I.; Darland, T.; Suchland, K. L.; Pasumamula,
S.; Kennedy, J. L.; Olson, S. B.; Magenis, R. E.; Amara, S. G.;
Grandy, D. K. Amphetamine, 3,4-methylenedioxymethamphetamine,
lysergic acid diethylamide, and metabolites of the catecholamine
neurotransmitters are agonists of a rat trace amine receptor. Mol.
Pharmacol. 2001, 60 (6), 1181-8.
(4) Borowsky, B.; Adham, N.; Jones, K. A.; Raddatz, R.; Artymyshyn,
R.; Ogozalek, K. L.; Durkin, M. M.; Lakhlani, P. P.; Bonini, J. A.;
Pathirana, S.; Boyle, N.; Pu, X.; Kouranova, E.; Lichtblau, H.; Ochoa,
F. Y.; Branchek, T. A.; Gerald, C. Trace amines: identification of a
family of mammalian G protein-coupled receptors. Proc. Natl. Acad.
Sci. U.S.A. 2001, 98 (16), 8966-71.
2-(4-Phenoxyphenyl)but-3-yn-1-amine Hydrochloride (23).
Refer to general procedure for Curtius rearrangement described
above. The crude product was purified via flash SiO2 chromatog-
raphy [eluted with methanol/ethyl acetate (1:4)] to give the pure
1
product 23 as a white solid (71 mg, 38% yield). H NMR (400
MHz, DMSO-d6) δ 7.99 (s, 3H), 7.44 (t, J ) 8.8 Hz, 2H), 7.40 (d,
J ) 8.4 Hz, 2H), 7.16 (t, J ) 7.4 Hz, 1H), 7.03 (m, 4H), 4.08 (t,
J ) 6.0 Hz, 1H), 3.50 (d, J ) 2.6 Hz, 1H), 3.12 (m, 2H). HRMS
(EI+) m/z for C16H15NO [M + H]+: calcd, 237.1154; found,
237.1149.
2-(1-Phenoxynaphthalen-4-yl)ethylamine (24). Refer to general
procedure for reduction of nitrile to amine hydrochloride: 0.13 g,
54% yield. 1H NMR (400 MHz, methanol-d4) δ 8.24 (d,
J ) 8.8 Hz, 1H), 8.12 (d, J ) 8.8 Hz, 1H), 7.66 (app t, J ) 7.6 Hz,
1H), 7.55 (app t, J ) 7.6 Hz, 1H), 7.36 (m, 3H), 7.13 (app t, J )
7.3 Hz, 1H), 7.02 (d, J ) 7.3 Hz, 2H), 6.88 (d, J ) 7.8 Hz, 1H),
3.43 (t, J ) 7.6 Hz, 1H), 3.27 (t, J ) 7.3 Hz, 2H). HRMS
(EI+) m/z for C18H17NO [M + H]+: calcd, 264.1388; found,
264.1393.
2-(1-Hydroxynaphthalen-4-yl)-2-phenylethylamine Hydro-
chloride (25). To a solution of 26 (0.24 g, 0.77 mmol) in dry CHCl3
(7 mL) at 0 °C was added BBr3 (2.43 mL, 1.0 M solution in DCM).
After stirring for 1 h at room temperature, the reaction was cooled
to 0 °C and anhydrous MeOH (7.65 mL) was added. The reaction
was refluxed in an open mouth flashed for 20 min before
evaporation of the solvent. The crude mixture was diluted with
EtOAc and made alkaline with potassium carbonate. The organic
layer was washed with water and brine, dried over MgSO4, filtered,
and concentrated under reduced pressure. Treatment with 3 N
anhydrous HCl in ethyl acetate and exposure to diethyl ether
precipitated the hydrochloride salts of 25 as a brownish solid (0.16
(5) Lindemann, L.; Ebeling, M.; Kratochwil, N. A.; Bunzow, J. R.;
Grandy, D. K.; Hoener, M. C. Trace amine-associated receptors form
structurally and functionally distinct subfamilies of novel G protein-
coupled receptors. Genomics 2005, 85 (3), 372-85.
(6) Pine, S. H.; Sanchez, B. L. Formic acid-formaldehyde methylation
of amines. J. Org. Chem. 1971, 36 (6), 829-32.
(7) Mattingly, P. G. Mono-Protected Diamines-NR-tert-Butoxycarbonyl
R,ω-Alkanediamine Hydrochlorides from Amino-alcohols. Synthesis
1990, (4), 366-368.
(8) Kraxner, J.; Hubner, H.; Gmeiner, P. Azepino- and diazepinoin-
doles: Synthesis and dopamine receptor binding profiles. Arch.
Pharm. 2000, 333 (9), 287-292.
(9) Shah, J. H.; Izenwasser, S.; Geter-Douglass, B.; Witkin, J. M.;
Newman, A. H. (()-(N-alkylamino)benzazepine analogs: novel
dopamine D1 receptor antagonists. J. Med. Chem. 1995, 38 (21),
4284-93.
(10) Evans, D. A.; Katz, J. L.; West, T. R. Synthesis of Diaryl Ethers
through the Copper-Promoted Arylation of Phenols with Arylboronic
Acids. An Expedient Synthesis of Thyroxine. Tetrahedron Lett. 1998,
39 (19), 2937-2940.

2798 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 12
Tan et al.
(11) Finholt, A. E.; Bond, A. C.; Schlesinger, H. I. Lithium Aluminum
Hydride, Aluminum Hydride and Lithium Gallium Hydride, and
Some of their Applications in Organic and Inorganic Chemistry. J.
Am. Chem. Soc. 1947, 69 (5), 1199-1203.
(12) Kruse, L. I.; Kaiser, C.; DeWolf, J. W. E.; Chamber, P. A.; Goodhart,
P. J.; Ezekiel, M.; Ohlstein, E. H. â-Substituted Phenethylamines as
High-Affinity Mechanism-Based Inhibitors of Dopamine â-Hydroxy-
lase. J. Med. Chem. 1988, 31 (4), 704-706.
(13) Eglen, R. M. Enzyme fragment complementation: a flexible high
throughput screening assay technology. Assay Drug DeV. Technol.
2002, 1 (1, Pt. 1), 97-104.
(14) Eglen, R. M.; Singh, R. Beta galactosidase enzyme fragment
complementation as
a novel technology for high throughput
screening. Comb. Chem. High Throughput Screening 2003, 6 (4),
381-7.
(15) Wainscott, D. B.; Little, S. P.; Yin, T.; Tu, Y.; Rocco, V. P.; He, J.
X.; Nelson, D. L. Pharmacologic characterization of the cloned human
trace amine-associated receptor1 (TAAR1) and evidence for species
differences with the rat TAAR1. J. Pharmacol. Exp. Ther. 2007, 320
(1), 475-85.
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