Trace amine-associated receptor agonists: Synthesis and evaluation of thyronamines and related analogues

Article abstract of DOI:10.1021/jm0505718

We have previously shown that several thyronamines, decarboxylated and deiodinated metabolites of the thyroid hormone, potently activate an orphan G protein-coupled receptor in vitro (TAAR1) and induced hypothermia in vivo on a rapid time scale [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), 638-642]. Herein, we report the synthesis of these thyronamines. Additionally, a large number of thyroamine derivatives were synthesized in an effort to understand the molecular basis of TAAR1 activation and hypothermia induction. Several derivatives were found to potently activate both rTAAR1 and mTAAR1 in vitro (compounds 77, 85, 91, and 92). When administered to mice at a 50 mg/kg dose, these derivatives all induced significant hypothermia within 60 min and exhibited a hypothermic induction profile analogous to 3-iodothyronamine (1, T₁AM) except 91, which proved to be more efficacious. On the basis of this result, a dose-dependent profile for 91 was generated and an ED₅₀ of 30 μmol/kg was calculated. Compound 91 proved to be more potent than T₁AM for TAAR1 activation and exhibits increased potency and efficacy for hypothermia induction. These data further strengthen the pharmacological correlation linking TAAR1 activation by thyronamines and hypothermia induction in mice.

Full text of DOI:10.1021/jm0505718

J. Med. Chem. 2006, 49, 1101-1112
1101
Trace Amine-Associated Receptor Agonists: Synthesis and Evaluation of Thyronamines and
Related Analogues
Matthew E. Hart,† Katherine L. Suchland,‡ Motonori Miyakawa,† James R. Bunzow,‡ David K. Grandy,‡ and
Thomas S. Scanlan*,†
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 & Science
UniVersity, 3181 Southwest Sam Jackson Park Road, Mail Code L334, Portland, Oregon 97239
ReceiVed June 16, 2005
We have previously shown that several thyronamines, decarboxylated and deiodinated metabolites of the
thyroid hormone, potently activate an orphan G protein-coupled receptor in vitro (TAAR1) and induced
hypothermia in vivo on a rapid time scale [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), 638-642]. Herein, we report the synthesis of these thyronamines.
Additionally, a large number of thyroamine derivatives were synthesized in an effort to understand the
molecular basis of TAAR1 activation and hypothermia induction. Several derivatives were found to potently
activate both rTAAR1 and mTAAR1 in vitro (compounds 77, 85, 91, and 92). When administered to mice
at a 50 mg/kg dose, these derivatives all induced significant hypothermia within 60 min and exhibited a
hypothermic induction profile analogous to 3-iodothyronamine (1, T1AM) except 91, which proved to be
more efficacious. On the basis of this result, a dose-dependent profile for 91 was generated and an ED50 of
30 µmol/kg was calculated. Compound 91 proved to be more potent than T1AM for TAAR1 activation and
exhibits increased potency and efficacy for hypothermia induction. These data further strengthen the
pharmacological correlation linking TAAR1 activation by thyronamines and hypothermia induction in mice.
Introduction
more potent inhibition of inotropy than chronotropy. Herein,
we describe the synthesis and properties of a number of
thyronamines and related analogues. These compounds were
screened in vitro for TAAR1 activation, and selected compounds
were evaluated in vivo for induction of hypothermia.
Thyroid hormone (TH) is crucial for normal physiology and
development in vertebrates.2 The predominant secreted form of
TH is thyroxine (T4; Figure 1), which is deiodinated in target
tissue to 3,5,3′-triiodothyronine (T3; Figure 1), the high-affinity
ligand for thyroid hormone receptors (TRs). The TRs regulate
TH target gene transcription in a T3-dependent manner, and like
all transcriptional regulation, these processes occur on a
relatively slow time scale. However, there are many rapid effects
associated with TH, especially in the cardiovascular system, that
occur in seconds to minutes, a time scale precluding a T3-TR
transcriptional mechanism.3,4 Some examples of these nonge-
nomic effects include sodium channel activation5 and increased
isolated cardiac myocyte contractile function.6 Additionally,
there is evidence that rapid effects of TH could have therapeutic
implications.7 Patients suffering from congestive heart failure
can experience a rapid increase in cardiac performance upon a
bolus injection of T3.
Recently, we demonstrated that a novel metabolite of the TH,
3-iodothyronamine (1, T1AM; Figure 1), elicited rapid responses
in vitro and in vivo.1 In HEK293 cells expressing an orphan G
protein-coupled receptor, the trace amine receptor8,9 (TAR)-
now officially referred to as the trace amine-associated receptor
(TAAR)10-T1AM potently increased cAMP accumulation
(rTAAR1, EC50 ) 14 nM; mTAAR1, EC50 ) 112 nM). In mice,
T1AM rapidly induces hypothermia and bradycardia and leads
to behavioral inactivity. In a rat working heart preparation, T1-
AM treatment leads to a rapid decrease in cardiac drive with a
Results and Discussion
Synthesis. Utilizing a divergent synthetic route, we synthe-
sized the entire panel of thyronamines from commercially
available starting materials. Synthesis of the right-hand portion
of the scaffold begins with the protection of tyramine 2 to give
3 (Scheme 1). Selective iodination of 3 was a crucial component
to our synthetic route, and many electrophilic iodine sources
were screened.11-13 We found that in situ generation of ICl in
methanol gave a mixture of the mono- and diiodinated products
4 and 5 favoring the former (method A).14 The diiodinated
product 5 can be synthesized in good yields with an excess of
iodine monochloride and butylamine (method B). The synthesis
of the left-hand portion of the scaffold begins with the protection
of commercially available phenol 6 as either the silyl ether 7
or the MOM-protected 8. The aryl bromides were lithiated
followed by reaction with triisopropyl borate to give the desired
boronic acids 9 and 10.15,16
With the appropriate boronic acid and phenols in hand, the
biaryl ether moiety was constructed. Boronic acid 9 was coupled
with phenols 3-5 utilizing stoichiometric copper(II) acetate to
give ethers 11-13, respectively (Scheme 2).17-19 In our hands,
this coupling procedure proved to be variable with good to
moderate yields reported. The ethers were treated with tetrabu-
tylammonium fluoride, and the resulting phenols were iodinated.
Utilizing method A outlined above for phenol 16 proved to be
problematic. An inseparable impurity arising from iodination
adjacent to the biaryl ether bridge contaminated the desired
* To whom correspondence should be addressed. Tel: 415-476-3620.
Fax: 415-502-7220. E-mail: scanlan@cgl.ucsf.edu.
† University of California at San Francisco.
‡ Oregon Health & Science University.
10.1021/jm0505718 CCC: $33.50 © 2006 American Chemical Society
Published on Web 01/11/2006

1102 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3
Hart et al.
Figure 1. Predominant TH produced by the thyroid gland, thyroxine (T4); the active TH, 3,3′,5-triiodothyronine (T3); and a novel metabolite,
3-iodothyronamine (1, T1AM).
Scheme 1. Synthesis of Thyronamine Fragmentsa
a Reagents and conditions: (a) Boc2O, NaHCO3, THF/H2O, room temperature. (b) NaI, NaOCl, KOH, MeOH, 0 °C. (c) ICl, BuNH2, DCM, 0 °C. (d)
TIPSCl, imidazole, DCM, room temperature. (e) NaH, MOMCl, THF, room temperature. (f) (i) n-BuLi, THF, -78 °C; (ii) B(OiPr)3, THF, -78 °C to room
temperature; (iii) 0.5 M HCl, 0 °C.
Scheme 2. Synthesis of Thyronaminesa
a Reagents and conditions: (a) Cu(OAc)2, 9, Et3N, pyridine, 4 Å powdered molecular sieves, DCM, room temperature. (b) TBAF, THF, 0 °C. (c) KI3,
BuNH2, THF/H2O, 0 °C. (d) ICl, BuNH2, THF, 0 °C. (e) 3 N HCl (anhydrous) in EtOAc.
product. However, KI3 and butylamine provided the requisite
monoiodinated product, albeit in low yields.20 Deprotection of
14-22 with 1-3 N HCl in anhydrous ethyl acetate gave the
desired thyronamines 23 (T0AM), 1 (T1AM), 24 (T2AM), 25
(3′-T1AM), 26 (3′,5′-T2AM), 27 (3,3′-T2AM), 28 (rT3AM), 29
(T3AM), and 30 (T4AM) in excellent yields.21 In all cases, the
hydrochloride salts were sufficiently pure and required no
additional purification.
the amine functionality, alkylation or modification of the amine,
and replacement of the 3-iodo substituent with an alkyl group.
Protected tyramine 3 was coupled with phenyl boronic acid
utilizing the copper(II)-mediated procedure outlined above to
give biaryl ether 31 (Scheme 3). Deprotection gave the
hydrochloride salt of the des-hydroxythyronamine 32. Alkylation
of 3 with a variety of aryl-substituted alkyl halides followed
by subsequent deprotection gave derivatives 38-42, with an
increased chain between the two aryl rings. In an effort to
examine the steric and electronic requirements of the distal aryl
ring, protected tyramine 3 was alkylated with a variety of
substituted benzyl halides followed by subsequent deprotection
providing derivatives 50-56.
In an effort to explore the structural requirements of TAAR1
activation, several derivatives of the thyronamines were pursued.
These analogues included removal of the phenol hydroxyl, an
increase in the distance between the two aryl rings, a change in
the electronic and steric requirements on the aryl ring distal to

Synthetic Trace Amine Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3 1103
Scheme 3. Synthesis of O-Substituted Analoguesa
a Reagents and conditions: (a) Phenyl boronic acid, Cu(OAc)2, Et3N, pyridine, 4 Å powdered molecular sieves, DCM, room temperature. (b) 3 N HCl
(anhydrous) in EtOAc. (c) Ph(CH2)nBr (n ) 1-4) or PhCdOCH2Br, K2CO3, DMF. (d) ArCH2Br, K2CO3, DMF.
Scheme 4. Alkylated Amine Derivativesa
a Reagents and conditions: (a) RBr, K2CO3, DMF, room temperature. (b) 3 N HCl (anhydrous) in EtOAc. (c) Formic acid, formaldehyde, reflux.
The benzylated intermediate 33 was alkylated with a variety
of alkyl halides in the presence of potassium carbonate in DMF
to give 57-61 in moderate yields (Scheme 4). Deprotection
with 3 N HCl in anhydrous ethyl acetate gave 62-66 as white
solids in excellent yields. The hydrochloride salts were suf-
ficiently pure and used without any further purification. Treat-
ment of 38 under Eschwieler-Clark conditions followed by
treatment with anhydrous HCl gave the dimethylated derivative
67 in acceptable yields.
To examine the requirement of the amine, we synthesized a
derivative replacing this functionality with a hydroxyl (Scheme
5). Commercially available phenol 68 was iodinated in the
presence of iodine monochloride and butylamine to give 69 in
low yields. Copper(II)-mediated coupling with boronic acid 9
gave 70 in moderate yields. Reduction of the ester under
standard diisobutyl aluminum hydride conditions, followed by
deprotection with tetrabutylammonium fluoride, gave 72 in good
yield.
condensed with nitromethane to give the nitro compound 74.22
Reduction with lithium aluminum hydride followed by protec-
tion gave 75 in respectable yields.22 Copper(II)-mediated
coupling of 75 with boronic acid 10 gave the biaryl ether 76.
Concomitant hydroxyl and amine deprotection in the presence
of 3 N anhydrous HCl in ethyl acetate gave derivative 77 in
excellent yields.
The second generation thyronamines that were synthesized
incorporated elements from T1AM and the first generation
derivatives described above. In particular, we wanted to
investigate combinations of electron-withdrawing groups on the
aryl ring distal to the amine, the iodine on the aryl ring proximal
to the amine, and N-alkylation. We examined both O-benzyl
tyramine and thyroanmine scaffolds with these modifications.
To this end, the iodinated tyramine intermediate 4 was
alkylated with either benzyl bromide or 4-trifluoromethylbenzyl
bromide under standard conditions to give 78 and 79, respec-
tively, in acceptable yields (Scheme 6). The alkylated product
78 and intermediate 48 described above were N-alkylated in
the presence of sodium hydride and iodomethane to give 80
We also synthesized a T1AM derivative replacing the 3-iodo
substituent with a methyl group (Scheme 5). Aldehyde 73 was

1104 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3
Scheme 5. Synthesis of 3-Iodothyronamine Analoguesa
Hart et al.
a Reagents and conditions: (a) ICl, BuNH2, THF, -40 °C. (b) Cu(OAc)2, 9, Et3N, Pyr, DCM, 4 Å molecular sieves. (c) DIBAL-H, THF, -78 °C. (d)
TBAF, THF, 0 °C. (e) CH3NO2, NH4OAc, reflux. (f) (i) LiAlH4, THF, reflux; (ii) Boc2O, NaHCO3, THF/H2O. (g) Cu(OAc)2, 10, EtNiPr2, pyridine, DCM,
4 Å molecular sieves, room temperature. (h) 3 N HCl (anhydrous in EtOAc).
Scheme 6. Synthesis of Second Generation Analoguesa
a Reagents and conditions: (a) Benzyl bromide, K2CO3, DMF. (b) NaH, MeI, THF, room temperature. (c) 3 N HCl (anhydrous) in EtOAc. (d) Aryl
boronic acid, Cu(OAc)2, pyridine, Et3N, DCM, 4 Å molecular sieves.
and 81 in good yields. Intermediates 78-81 were deprotected
in the presence of 3 N HCl in anhydrous ethyl acetate to give
the hydrochloride salts 82-85 in excellent yields and were used
without any further purification.
and 88 in moderate yields. Ethers 87 and 88 were treated with
sodium hydride and iodomethane to give the N-alkylated
products 89 and 90. Intermediates 86, 89, and 90 were then
deprotected in the presence of 3 N HCl in anhydrous ethyl
acetate to give the corresponding hydrochloride salts 91-93 in
excellent yields. Finally, N-t-Boc-3-iodothyronamine 12 was
treated with sodium hydride and iodomethane; however, the
desired N-alkylated product 94 was only a minor product. The
To examine the biaryl ether scaffold, the iodinated tyramine
4 was subjected to the copper(II)-mediated coupling conditions
described above in the presence of either phenyl-, p-fluorophen-
yl-, or p-trifluoromethylphenyl boronic acid to give 86, 87,

Synthetic Trace Amine Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3 1105
Table 2. First Generation Analogues of Thyronamines Activate
rTAAR1 and mTAAR1
Figure 2. Dose-dependent cAMP accumulation. Curves representing
dose-dependent increase in cAMP accumulation in cultured HEK293
cells stably expressing rTAAR1. Data reported for 3-iodothyronamine
1 (T1AM) (b), O-phenyl-3-iodotyramine 91 (O), and O-(p-trifluoro-
methyl)benzyl tyramine 55 (4) are expressed as a percent of a forskolin
control (%FSK). Concentration-response curves were plotted, and EC50
values were calculated with Prism software as described in the
Experimental Section. The standard error of the mean was less than
0.1 log units from the average EC50 value in all cases.
Table 1. Thyronamines Activate rTAAR1 and mTAAR1
EC50
#
R1
R2
R3
R4
rTAAR1
mTAAR1
23
1
H
I
I
I
I
H
H
H
H
H
H
I
I
I
I
I
H
H
H
H
H
H
I
H
I
I
H
H
H
I
I
I
I
I
I
131
14
56
87
>1000
41
>1000
>1000
800
∼1000
112
24
29
30
27
28
26
25
371
>1000
>1000
∼1000
>1000
>1000
>1000
H
a Values represent the average EC50 of multiple experiments and were
calculated using Prism software as described in the Experimental Section.
The standard error of the mean was less than 0.1 log units from the average
EC50 value in all cases.
predominate product, 95, resulted from hydride-promoted desi-
lylation followed by subsequent methylation of the phenol.
These products were subsequently deprotected in the presence
of 3 N HCl in anhydrous ethyl acetate to give the corresponding
hydrochloride salts, 96 and 97.
Receptor Activation. Previously, we reported rTAAR1 and
mTAAR1 activation by thyronamines.1 Both mTAAR1 and
rTAAR1 are GRs-coupled G protein-coupled receptors that in
vitro stimulate adenylyl cyclase leading to cAMP accumulation
in response to agonists. A typical dose-response curve for 1,
T1AM, is shown in Figure 2. As the results for the thyronamines
indicate, the number of iodines on the scaffold and relative
position directly affect potency (Table 1). T1AM was the most
potent at both rTAAR1 and mTAAR1, with EC50 values of 14
and 112 nM, respectively.
The first generation thyronamine analogues described above
were evaluated in the cAMP accumulation assay with cells
stably expressing either rTAAR1 or mTAAR1 (Table 2). The
O-phenyltyramine derivative 32 exhibited increased potency at
TAAR1 of both species as compared to 23, T0AM (by
approximately 3-fold). Increasing the distance between the two
aryl rings resulted in different potencies at rTAAR1 and
mTAAR1. The benzylated derivative 38 was less potent at
rTAAR1 than mTAAR1. The addition of another methylene
group in the spacer was also deleterious (compound 39);
a Values represent the average EC50 of multiple experiments and were
calculated using Prism software as described in the Experimental Section.
The standard error of the mean was less than 0.1 log unit from the average
EC50 value in all cases.
however, significant activity was rescued with a three or four
carbon spacer (compounds 40 and 41, respectively). Incorpora-

1106 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3
Hart et al.
Table 3. Second Generation Analogues of Thyronamines Activate
tion of a carbonyl in the spacer exhibited reduced potency at
rTAAR1 and increased potency at mTAAR1 (compound 42).
In general, the addition of bulky and/or electron-donating groups
to the benzyl group was tolerated by both rTAAR1 and
mTAAR1 (compounds 50-52). Incorporating electron-with-
drawing substituents on the benzyl group significantly increased
the potency toward TAAR1 (compounds 53-55), except for
the pentafluorobenzyl derivative 56, which was inactive. This
suggests that these derivatives may be forming an edge-to-π
interaction crucial for receptor activation.23,24 Of the benzyl
derivatives examined, the p-trifluoromethylbenzyl derivative 55
was the most potent toward rTAAR1 and mTAAR1 (calculated
EC50 values of 55 and 20.2 nM, respectively). A typical dose-
response curve for 55 vs rTAAR1 is shown in Figure 2.
rTAAR1 and mTAAR1
Because the TAAR1 is most closely related to the receptors
for the biogenic amines, we anticipated that the amine func-
tionality would be required for activation. The N-methylated
analogue of benzyl tyramine 38 (compound 62) exhibited
increased potency; however, larger alkyl substituents greatly
decreased activation of both rTAAR1 and mTAAR1 (com-
pounds 64-66). The notable exception is the ethyl-substituted
derivative 63, which was equipotent to 62 at mTAAR1 but
inactive against rTAAR1. N,N-Dimethylation was also deleteri-
ous for rTAAR1 activation while mTAAR1 exhibited moderate
activation (compound 67). In the case of compound 72, where
the amine has been replaced with a hydroxyl, no TAAR1
activation was observed.
Replacement of the 3-iodo substituent with an alkyl isostere
was also examined. Derivative 77 with a methyl group at the
3-position of the thyronamine scaffold was nearly as potent as
T1AM against both rTAAR1 and mTAAR1 (calculated EC50
values of 33 and 116 nM, respectively).
a Values represent the average EC50 of multiple experiments and were
calculated using Prism software as described in the Experimental Section.
The standard error of the mean was less than 0.1 log unit from the average
EC50 value in all cases.
The second generation analogues were also assayed for
rTAAR1 and mTAAR1 activation (see Table 3). The benzyl-
substituted tyramine derivative 82 with the iodine exhibited an
increase in rTAAR1 activation and slightly attenuated mTAAR1
activation relative to the parent compound 38. However,
inclusion of the iodine and methylation of the amine, compound
84, led to an increase in potency of activation for TAAR1.
Interestingly, 83, which contained an electron-withdrawing
group, a trifluoromethyl, and the iodine, failed to activate
rTAAR1 significantly and only weakly activated mTAAR1.
However, 85, which contained the same electron-withdrawing
group and the methylated amine, potently activated both
rTAAR1 and mTAAR1 (calculated EC50 values of 61 and 12
nM, respectively). The N-methylated T1AM derivative 96
exhibited slightly increased potency relative to T1AM at
rTAAR1 (In a comparative study, T1AM exhibited an EC50 of
25 nM) but slightly attenuated potency at mTAAR1. Methylation
of the phenol, derivative 97, was deleterious to mTAAR1 and
rTAAR1 activation. Replacing the phenolic hydroxyl with a
large electron-withdrawing group was also deleterious. Com-
pound 93 failed to activate the two TAARs examined to a
significant level. However, compound 92, which contains a
fluorine atom, exhibited increased potency at both rTAAR1 and
mTAAR1. The derivative lacking the phenolic hydroxyl 91 was
the most potent agonist of heterologously expressed rTAAR1
and one of the most potent at heterologously expressed
mTAAR1 (calculated EC50 values of 2.4 and 35 nM, respec-
tively). A typical dose-response curve for 91 activation of
rTAAR1 is shown in Figure 2.
compounds 77, 85, 91, and 92, were also examined for
hypothermia induction in mice. When adult male C57BL/6J
mice were administered a 50 mg/kg dose of 77, 85, 91, and 92
(i.p.), rapid induction of hypothermia was observed (Figure 3A).
Furthermore, all four of the compounds induced a significant
drop in body temperature relative to vehicle control and similar
to the degree of hypothermia seen with 50 mg/kg T1AM.
Compounds 77, 85, and 92 were as efficacious as T1AM at this
dose with mean minimal body temperatures of 29.6, 26.7, and
28.3 °C, respectively. Mice treated with T1AM typically reached
a minimal body temperature of 28.5 °C. Compound 91 was more
efficacious than T1AM, dropping the average body temperature
of the mice from 36.7 to 23.6 °C within 120 min; however,
this derivative proved to be toxic at this dose. After 24 h, the
mice treated with 91 exhibited stiffening of the hind limbs and
several expired (died). Similarly, those mice administered
derivative 85 became cold, assumed a hunched posture, and
had distended abdomens 8 days after injection, at which time
the animals were euthanized.
A dose range study was performed with 91 but not with the
other derivatives because of the observed toxicity. Mice were
treated with 2, 10, 25, and 50 mg/kg doses of 91 (Figure 3B).
Mice administered 25 and 50 mg/kg doses exhibited significant
hypothermia relative to the vehicle control. On the basis of the
above data, we calculated the dose to induce half-maximal
stimulation of hypothermia (ED50) for 91 to be 30 µmol/kg.
This compares with the 59 µmol/kg ED50 of T1AM for
hypothermia induction.
In Vivo Pharmacology. We previously reported that in mice,
T1AM induced a rapid, dose-dependent drop in core body
temperature.1 The most potent derivatives from this study,
Discussion. We previously showed that certain thyronamines
proposed to arise from deiodination and decarboxylation of T4
are potent agonists of mouse and rat TAAR1.1 3-Iodothy-

Synthetic Trace Amine Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3 1107
linker length is a useful property as we found that the O-benzyl
compounds (containing a linker length of two atoms) were
significantly easier to prepare than the diaryl ether thyronamine
derivatives (containing a one atom linker). In terms of the SAR,
this suggests flexibility in the TAAR1 ligand-binding pocket
where ligands that are longer than thyronamines can be
accommodated. Although the ability to substitute methyl for
iodide at the 3-position of the inner ring is not unusual, it is
somewhat surprising that this substitution does not lead to a
decrease in potency. In the context of the nuclear TRs, a similar
methyl for iodine substitution results in a 100-fold decrease in
agonist potency.25 Finally, the observation that the 4′-OH of
the thyronamine is not required is also divergent from the
thyronine/nuclear TR SAR where removal of the 4′-OH results
in about a 10-fold decrease in binding affinity and potency.25
In addition, the 4′-OH is an important site of sulfation and
glucoronidation, which are important clearance mechanisms.26
Compounds 77, 85, 91, and 92 were found to be more potent
agonists at either rat or mouse TAAR1 than 1 (T1AM). Upon
administration to mice, all of these compounds induced hypo-
thermia with the same rapid kinetics as T1AM. In addition, all
of the compounds except 91 lowered body temperature to the
same level as T1AM. Compound 91 was found to have greater
efficacy of hypothermia induction than T1AM and in a dose
ranging study was found to be more potent than T1AM by a
factor of 2. This further strengthens the pharmacological
correlation linking TAAR1 activation by thyronamines and
hypothermia induction in mice.1 Compounds 85, 91, and 92 all
exhibited obvious toxicity within a week of the hypothermia
measurements; this was not seen with T1AM. A common
structural feature of these three derivatives is the lack of a 4′-
OH, which as mentioned above is the site of sulfation/
glucoronidation modification in thyronines, and, by analogy,
may play a similar role in the clearance mechanism for
thyronamines. We speculate, therefore, that impaired clearance
may be a factor in the observed toxicity of these compounds.
Figure 3. Effect of thyronamine analogues on rectal temperature of
mice. (A) Effects of intraperatoneal injection (i.p.) of compounds 77
(O), 85 (3), 91 (1), and 92 (0) at 50 mg/kg as compared to 1 (T1AM)
(50 mg/kg, [) and vehicle control (100 µL of DMSO, b) in adult
male C57BL/6J mice maintained at 25 °C. The baseline temperature
is determined immediately before each mouse was injected (time 0
min). All compounds significantly reduced the rectal temperature as
compared to vehicle control. (B) Compound 91 reduces the rectal
temperature in a dose-dependent manner. Effects of i.p. injection of
91 at 2, 10, 25, and 50 mg/kg as compared to vehicle control (200 µL
of DMSO, b) in adult male C57BL/6J mice maintained at 25 °C. Data
reported for compounds 77, 85, 91, and 92 are averages of 2-4 mice.
ronamine (1, T1AM) was found to be the most potent agonist
for both mouse and rat TAAR1 and was also found to be an
endogenous component of extracts from rodent brain, peripheral
organs, and blood. In pharmacological studies, T1AM (and 23,
T0AM) rapidly induces hypothermia and bradycardia in mice
and rapidly reduces cardiac output in an ex vivo working rat
heart preparation. The purpose of the present study was to
understand the structure-activity relationship (SAR) of thy-
ronamine/TAAR activation, and toward this goal, a large number
of thyronamine derivatives were synthesized and evaluated as
TAAR1 agonists.
Analysis of the TAAR1 activation data reported herein
suggests the following requirements for TAAR activation: (i)
A basic amino group at CR is required; (ii) monomethylation
of the amine can be beneficial although larger alkyl groups and
bis-alkylation are deleterious; (iii) mTAAR1 and rTAAR1 differ
with respect to their tolerance of changes in the diaryl linker,
both in length and in functionality; (iv) within the thyronamine
scaffold, an iodine or methyl substituent at the 3-position is
optimal; and (v) H at the 4′-position vs OH is optimal, and
substituents larger than OH are deleterious.
Summary
In summary, the synthesis of a family of decarboxylated TH
analogues, called thyronamines, is reported. Additionally, we
synthesized a family of thyronamine derivatives to explore the
SAR of TAAR1 activation and induced hypothermia in mice.
In the case of rTAAR1 activation, derivatives 77, 91, and 92
were the most potent. In the case of mTAAR1, derivatives 85,
91, and 92 were among the most potent. When administered to
mice at a 50 mg/kg dose, these derivatives all induced significant
hypothermia within 60 min. All of these derivatives exhibited
a hypothermic induction profile analogous to 2, T1AM, except
91, which proved to be more efficacious. On the basis of this
result, a dose-dependent profile for 91 was generated and an
ED50 of 30 µmol/kg was calculated. The data for 91 taken as a
whole indicate that it is more potent then T1AM for TAAR1
activation and exhibits increased potency and efficacy for
hypothermia induction.
The requirement for a basic amine at CR is consistent with
the SARs of other biogenic amine GPCRs that belong to the
same family as the TAARs. Likewise, the toleration of N-
alkylation is consistent although somewhat more limited in the
case of TAAR1. For example, isoproterenol, which carries an
N-isopropyl substituent, is a substantially more potent â-adren-
ergic receptor agonist than the endogenous ligand norepine-
phrine, whereas monomethylation marks the rough limit for
N-alkylation of thyronamine/TAAR1 agonists and only a modest
potency improvement is seen. The observed sensitivity to diaryl
Materials and Methods
General. 1H and 13C NMR spectra were taken on a Varian 400
(400 and 100 MHz, respectively). Data reported were calibrated to
internal TMS (0.0 ppm) for all solvents unless otherwise noted and
are reported as follows: chemical shift, multiplicity (app, apparant;
par obsc, partially obscured; ovrlp, overlapping; br, broad; s, singlet;
d, doublet; t, triplet; q, quartet; and m, multiplet), coupling constant,
and integration. High-resolution mass spectrometry (HRMS) using
electrospray ionization was performed by the National Bio-Organic,
Biomedical Mass Spectrometry Resource at UCSF. Inert atmosphere

1108 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3
Hart et al.
operations were conducted under argon passed through a Drierite
drying tube in flame-dried or oven-dried glassware unless otherwise
noted. Anhydrous THF, DCM, diethyl ether, pyridine, and diiso-
propyl ethylamine 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 J. C.
Meyer (University of California, Irvine). Anhydrous DMF was
obtained by passing through two columns of activated molecular
sieves. All other anhydrous solvents and reagents were purchased
from Aldrich, Sigma-Aldrich, Fluka, or Acros and were used
without any further purification unless otherwise stated. Final
was washed with 0.5 M HCl, and the aqueous phase was extracted
with ethyl acetate. The combined organic layers were sequentially
washed with water and brine and then dried over MgSO4. The crude
product was purified as described below.
Thyronamine Hydrochloride (23, T0AM). Refer to the general
procedure for t-Boc deprotection described above. The crude
reaction mixture was concentrated in vacuo and dried under high
vacuum pressure to give 23 as a slightly tan solid (32.9 mg, 100%
1
yield). H NMR (400 MHz, DMSO-d6): δ 9.37 (s, 1 H), 7.90 (br
s, 3 H), 7.20 (d, J ) 8.4 Hz, 1 H), 6.86 (ovrlp d, J ) 8.8 Hz, 1 H),
6.85 (ovrlp d, J ) 8.4 Hz, 1 H), 6.78 (d, J ) 8.8 Hz, 1 H), 2.99
(app br q, J ) 8.0 Hz, 2 H), 2.81 (t, J ) 8.2 Hz, 2 H). HRMS
(EI+, free base) m/z for C14H15NO2: calcd, 229.1103; found,
229.1107. LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 4.78 min; purity, 100%; [M - NH2]+
calcd, 213.09; found, 213.37 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 3.22 min; purity, 95%.
1
compounds were judged to be >95% pure by H NMR analysis
and confirmed by LC/MS and HPLC. LC/MS was performed on
an Waters AllianceHT LC/MS with a gradient of 0-100% methanol
(0.05% TFA) over 7 min. HPLC was performed on a Waters
AllianceHT LC with a gradient of 0-100% acetonitrile (0.05%
TFA) over 7 min.
In Vitro cAMP Assays. HEK293 cells stably transfected with
either rTAAR1 or mTAAR1 were harvested in Krebs-Ringer-
HEPES buffer (KRH) and preincubated in KRH with 200 µM
3-isobutyl-1-methylxanthine (IBMX). Cells were incubated in KRH
with 100 µM IBMX with the test compound, forskolin (10 µM),
or vehicle (DMSO) for 1 h at 37 °C (400 µL total volume). The
cells were then boiled for 20 min after adding an equal volume of
0.5 mM sodium acetate buffer and centrifuged to remove cellular
debris. An aliquot of the resulting extract (200 µL) was analyzed
for cAMP content using competitive binding of [3H]cAMP to a
cAMP binding protein (Diagnostic Products Corp., Los Angeles,
CA). Data were reported relative to the forskolin control and
expressed as %cAMP. Concentration-response curves were plotted,
and EC50 values were calculated with Prism software (GraphPad,
San Diego, CA). The R2 values in all cases were greater than 0.9.
Experiments were run in triplicate, and the standard error of the
mean (SEM) was less than 0.1 log units from the average EC50
value in all cases.
In Vivo Induced Hypothermia. C57BL/6J male mice aged
about 7-10 weeks were obtained from Jackson Laboratories. Mice
were housed in groups of 3-6 per cage and had ad libitum access
to food (PMI rodent lab chow) and water. The vivarium was
maintained at 21-22 °C on a 12 h/12 h light/dark cycle with lights
on at 06:00. All studies were conducted between 09:30 and 13:30
in a room with an ambient temperature of 19-21 °C. All
experiments were done in accordance with approved institutional
and National Institutes of Health (NIH) guidelines for the use and
care of animals.
All drugs were dissolved in 100% dimethyl sulfoxide (DMSO)
with the exceptions of T1AM, which was dissolved in 60% DMSO
and physiological saline (pH7.4), and 91 (65% DMSO and
physiological saline). On the test day, before drug administration,
basal body weights and rectal temperatures (THM 100, Indus
Instruments) were determined. After basal measures, mice received
an i.p. injection of 77, 85, 91, 92, 1 (T1AM) (2, 10, 25, and 50
mg/kg), or vehicle (100% DMSO, 60% DMSO and 40% saline, or
65% DMSO and 35% saline) and were returned to the home cages.
The rectal temperature was measured at 30, 60, 120, 180, 240, and
1440 min after injection. Temperature data were analyzed by a two-
way analysis of variance (ANOVA). Significance was set at P <
0.05. After a significant overall ANOVA, Bonferroni posthoc
comparisons were done across the treatment groups.
General Procedure for t-Boc Deprotection. The protected
amine (31.2 mg, 0.054 mmol) was dissolved in a 1 or 3 N HCl
solution in ethyl acetate (2 mL, anhydrous), and the reaction mixture
was stirred at ambient temperature for 5-15 h. A white precipitate
formed after several minutes. Additional HCl was added as needed
(2 mL), and the reaction mixture was stirred until complete by TLC.
The reaction was completed as described below.
3-Iodothyronamine Hydrochloride (1, T1AM). Refer to the
general procedure for t-Boc deprotection described above. The crude
precipitate was filtered and washed with ether to give 1 as a white
1
solid (816 mg, 93% yield). H NMR (400 MHz, DMSO-d6): δ
9.44 (s, 1 H), 8.12 (br s, 3 H), 7.76 (s, 1 H), 7.20 (d, J ) 8.0 Hz,
1 H), 6.79 (s, 4 H), 6.68 (d, J ) 8.4 Hz, 1 H), 2.98 (app br q, J )
7.2 Hz, 2 H), 2.84 (t, J ) 7.4 Hz, 2 H). HRMS (EI+, free base)
m/z for C14H14INO2 [M - NH3]+: calcd, 337.9804; found,
337.9812. LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 5.32 min; purity, 100%; [M + H]+:
calcd, 356.01; found, 356.44 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 3.73 min; purity, 100%.
3,5-Diiodothyronamine Hydrochloride (24, T2AM). Refer to
the general procedure for t-Boc deprotection described above. The
crude reaction mixture was concentrated in vacuo and dried under
high vacuum pressure to give 24 as a white solid (26.7 mg, 96%
1
yield). H NMR (400 MHz, D2O): δ 7.97 (s, 2 H), 6.89 (d, J )
6.8 Hz, 2 H), 6.79 (d, J ) 7.2 Hz, 2 H), 3.29 (app t, J ) 6.4 Hz,
2 H), 3.01 (app t, J ) 6.4 Hz, 2 H). HRMS (EI+, free base) m/z for
C14H13I2NO2: calcd, 480.9036; found, 480.9050. LC/MS (LC:
gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention time,
5.45 min; purity, 100%; [M + H]+: calcd, 481.91; found, 482.30
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 3.91 min; purity, 95%.
3′-Iodothyronamine Hydrochloride (25, 3′-T1AM). Refer to
the general procedure for t-Boc deprotection described above. The
crude reaction mixture was concentrated in vacuo and dried under
high vacuum pressure to give 25 as a white solid (12.7 mg, 98%
yield). 1H NMR (400 MHz, DMSO-d6): δ 10.24 (s, 1 H), 7.86 (s,
3 H), 7.30 (d, J ) 2.4 Hz, 1 H), 7.23 (d, J ) 8.4 Hz, 2 H), 6.96-
6.86 (m, 4 H), 3.01 (br s, 2 H), 2.83 (app t, J ) 7.6 Hz, 2 H).
HRMS (EI+, free base) m/z for C14H14INO2 [M - NH3]+: calcd,
337.9804; found, 337.9809. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.48 min; purity, 100%;
[M + H]+: calcd, 356.01; found, 356.44 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 3.84 min; purity,
100%.
3′,5′-Diiodothyronamine Hydrochloride (26, 3′,5′-T2AM).
Refer to the general procedure for t-Boc deprotection described
above. The crude reaction mixture was diluted with ether, and the
precipitated product was collected via vacuum filtration to give 26
as a white solid (32.3 mg, 88% yield). 1H NMR (400 MHz, DMSO-
d6): δ 9.41 (s, 1 H), 7.95 (s, 3 H), 7.39 (s, 2 H), 7.27 (d, J ) 8.4
Hz, 2 H), 6.96 (d, J ) 8.4 Hz, 2 H), 3.02 (br s, 2 H), 2.86 (app br
t, J ) 8.0 Hz, 2 H). HRMS (EI+, free base) m/z for C14H13I2NO2
[M - NH3]+: calcd, 463.8770; found, 463.8748. LC/MS (LC:
gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention time,
5.83 min; purity, 100%; [M + H]+: calcd, 482.91; found, 482.30
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 4.18 min; purity, 100%.
General Procedure for Silyl Deprotection. To a stirred solution
of the protected phenol (1.0 mmol) in THF (10 mL) was added
TBAF (1.5 mL, 1.5 mmol, 1 M solution in THF) dropwise. The
reaction mixture was stirred for 10-30 min until complete by TLC
analysis and then diluted with ethyl acetate. The reaction mixture
3,3′-Diiodothyronamine Hydrochloride (27, 3,3′-T2AM). Refer
to the general procedure for t-Boc deprotection described above.
The crude reaction mixture was concentrated in vacuo and dried
under high vacuum pressure to give 27 as a white solid (14.6 mg,

Synthetic Trace Amine Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3 1109
1
100% yield). H NMR (400 MHz, DMSO-d6): δ 10.27 (s, 1 H),
O-(2′-Phenyl)ethyl-tyramine Hydrochloride (39). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the precipitate was
collected by vacuum filtration to give 39 as a white solid (22.4
7.96 (br s, 3 H), 7.79 (d, J ) 1.6 Hz, 1 H), 7.25 (ovrlp dd, J ) 8.4,
2.0 Hz, 1 H), 7.23 (ovrlp d, J ) 2.8 Hz, 1 H), 6.92 (ovrlp d, J )
8.8 Hz, 1 H), 6.87 (ovrlp dd, J ) 8.8, 2.8 Hz, 1 H), 6.81 (d, J )
8.0 Hz, 1 H), 3.03 (app br s, 2 H), 2.84 (br t, J ) 7.6 Hz, 2 H).
LC/MS (LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+):
retention time, 5.78 min; purity, 100%; [M + H]+: calcd, 481.91;
found, 482.24 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.15 min; purity, 98%.
3,3′,5′-Triiodothyronamine Hydrochloride (28, rT3AM). Refer
to the general procedure for t-Boc deprotection described above.
The crude reaction mixture was diluted with ether, and the white
precipitate was collected by vacuum filtration to give 28 as a white
1
mg, 93% yield). H NMR (400 MHz, DMSO-d6): δ 7.86 (br s, 3
H), 7.16-7.23 (m, 5 H), 7.12 (d, J ) 8.4 Hz, 2 H), 6.86 (d. J )
8.0 Hz, 2 H), 4.13 (t, J ) 6.8 Hz, 2 H), 2.98 (ovrlp t, J ) 7.0 Hz,
2 H), 2.40 (ovrlp app t, J ) 8.0 Hz, 2 H), 2.75 (app t, J ) 8.0 Hz,
2 H). HRMS (EI+, free base) m/z for C16H19NO: calcd, 241.1467;
found, 241.1457. LC/MS (LC: gradient 0-100% MeOH [0.05%
TFA], MS: EI+): retention time, 5.68 min; purity, 100%; [M +
H]+: calcd, 242.15; found, 242.49 m/z. HPLC (gradient 0-100%
MeCN [0.05% TFA]): retention time, 4.06 min; purity, 100%.
O-(3′-Phenyl)propyl-tyramine Hydrochloride (40). Refer to
the general procedure for t-Boc deprotection described above. The
crude reaction mixture was concentrated in vacuo and dried under
high vacuum pressure to give 40 as a white solid (80 mg, 98%
yield). 1H NMR (400 MHz, DMSO-d6): δ 8.06 (br s, 2 H), 7.33-
7.15 (m, 8 H), 6.88 (d, J ) 8.0 Hz, 2 H), 3.94 (br t, J ) 6.0 Hz,
2 H), 2.97 (app br t, J ) 8.4 Hz, 2 H), 2.81 (app br t, J ) 8.4 Hz,
2 H), 2.73 (app br t, J ) 6.0 Hz, 2 H), 2.02-1.99 (m, 2 H). 13C
NMR (100 MHz, methanol-d4): δ 160.0, 142.9, 130.08, 129.5,
129.4, 126.9, 116.0, 68.0, 42.1, 33.7, 32.2. HRMS (EI+, free base)
m/z for C17H21NO: calcd, 255.1623; found, 255.1619. LC/MS
(LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention
time, 5.95 min; purity, 100%; [M + H]+: calcd, 256.17; found,
256.50 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.30 min; purity, 100%.
1
solid (27.1 mg, 85% yield). H NMR (400 MHz, DMSO-d6): δ
9.39 (s, 1 H), 7.92 (br s, 3 H), 7.81 (d, J ) 2.0 Hz, 1 H), 7.29
(ovrlp dd, J ) 8.0, 2.0 Hz, 1 H), 7.29 (ovrlp s, 2 H), 6.95 (d, J )
8.4 Hz, 1 H), 3.05 (br s, 2 H), 2.85 (t, J ) 7.6 Hz, 2 H). LC/MS
(LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention
time, 6.10 min; purity, 100%; [M + H]+: calcd, 607.81; found,
608.24 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.49 min; purity, 99%.
3,3′,5-Triiodothyronamine Hydrochloride (29, T3AM). Refer
to the general procedure for t-Boc deprotection described above.
The crude reaction was concentrated in vacuo and dried under high
vacuum pressure to give 29 as a tan solid (9.6 mg, 100% yield).
1H NMR (400 MHz, DMSO-d6): δ 10.00 (s, 1 H), 7.86 (ovrlp s,
2 H), 7.80 (ovrlp br s, 3 H), 6.98 (d, J ) 2.8 Hz, 1 H), 6.83 (d, J
) 9.2 Hz, 1 H), 6.65 (dd, J ) 8.8, 3.2 Hz, 1 H), 3.11 (t, J ) 7.2
Hz, 2 H), 2.84 (t, J ) 7.2 Hz, 2 H). HRMS (EI+, free base) m/z for
C14H12I3NO2: calcd, 606.8002; found, 606.8010. LC/MS (LC:
gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention time,
5.90 min; purity, 100%; [M + H]+: calcd, 607.81; found, 608.16
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 4.35 min; purity, 95%.
O-(4′-Phenyl)butyl-tyramine Hydrochloride (41). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was concentrated in vacuo and dried under high
vacuum pressure to give 41 as a white solid (95 mg, 99% yield).
1H NMR (400 MHz, DMSO-d6): δ 8.01 (br s, 2 H), 7.28-7.14
(m, 8 H), 6.87 (d, J ) 8.0 Hz, 2 H), 3.94 (br t, J ) 6.0 Hz, 2 H),
2.94 (app br t, J ) 8.4 Hz, 2 H), 2.81 (app br t, J ) 8.4 Hz, 2 H),
2.62 (app br t, J ) 6.0 Hz, 2 H), 1.73-1.62 (m, 4 H). 13C NMR
(100 MHz, methanol-d4): δ 160.0, 143.5, 130.8, 129.6, 129.4, 129.3,
126.8, 68.9, 42.2, 36.6, 33.7, 29.9, 29.1. HRMS (EI+, free base)
m/z for C18H23NO [M - CH3NH + H]+: calcd, 240.1514; found,
240.1512. LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 6.18 min; purity, 100%; [M + H]+:
calcd, 270.19; found, 270.58 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 4.54 min; purity, 97%.
3,3′,5,5′-Tetraiodothyronamine Hydrochloride (30, T4AM).
Refer to the general procedure for t-Boc deprotection described
above. The crude reaction was concentrated in vacuo and dried
under high vacuum pressure to give 30 as a tan solid (13.8 mg,
1
100% yield). H NMR (400 MHz, DMSO-d6): δ 9.25 (s, 1 H),
7.87 (s, 2 H), 7.11 (s, 2 H), 3.12 (app br s, 2 H), 2.85 (t, J ) 7.2
Hz, 2 H). LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 6.12 min; purity, 100%; [M + H]+:
calcd, 733.70; found, 733.89 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 4.60 min; purity, 97%.
O-(Phenylmethanone)methyl-tyramine Hydrochloride (42).
Refer to the general procedure for t-Boc deprotection described
above. The crude reaction was diluted with ether, and the precipitate
was collected by vacuum filtration to give 42 as a white solild (45
O-Phenyl-tyramine Hydrochloride (32). Refer to the general
procedure for t-Boc deprotection described above. The crude
reaction was concentrated in vacuo and dried under high vacuum
pressure to give 32 as a tan solid (18.3 mg, 100% yield). 1H NMR
(400 MHz, DMSO-d6): δ 8.17 (br s, 3 H), 7.38 (app t, J ) 7.6 Hz,
2 H), 7.28 (d, J ) 8.4 Hz, 2 H), 7.13 (t, J ) 7.4 Hz, 1 H), 7.02-
6.94 (m, 4 H), 3.02 (app br t, J ) 8.0 Hz, 2 H), 2.90 (app t, J )
8.4 Hz, 2 H). HRMS (EI+, free base) m/z for C14H15NO: calcd,
213.1154; found, 213.1158. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.45 min; purity, 100%;
[M + H]+: calcd, 214.12; found, 214.46 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 3.79 min; purity,
100%.
1
mg, 99% yield). H NMR (400 MHz, DMSO-d6): δ 8.02 (app br
d, J ) 7.6 Hz, 2 H), 7.70 (t, J ) 7.6 Hz, 1 H), 7.58 (t, J ) 7.6 Hz,
2 H), 7.16 (d, J ) 8.8 Hz, 2 H), 6.93 (d, J ) 8.8 Hz, 2 H), 5.55 (s,
2 H), 2.98 (app br t, J ) 8.0 Hz, 2 H), 2.81 (app br t, J ) 6.0 Hz,
2 H). 13C NMR (100 MHz, methanol-d4): δ 196.9, 158.9, 135.1,
130.9, 130.5, 129.1, 116.3, 71.7, 42.9, 33.7. HRMS (EI+, free base)-
m/z for C16H17NO2 [M - CH4N + H]+: calcd, 226.0994; found,
226.0996. LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 4.93 min; purity, 100%; [M + H]+:
calcd, 256.13; found, 256.43 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 3.45 min; purity, 100%.
O-Benzyl-tyramine Hydrochloride (38). Refer to general
procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the white precipitate
was collected by vacuum filtration to give 38 as a white solid (156
mg, 97% yield). 1H NMR (400 MHz, DMSO-d6): δ 8.03 (s, 3 H),
7.46-7.30 (m, 5 H), 7.17 (app d, J ) 8.8 Hz, 2 H), 6.97 (app d,
J ) 8.4 Hz, 2 H), 5.08 (s, 2 H), 2.97 (app t, J ) 7.5 Hz, 2 H), 2.81
(app t, J ) 7.5 Hz, 2 H). HRMS (EI+, free base) m/z for C15H17-
NO: calcd, 227.1310; found, 227.1316. LC/MS (LC: gradient
0-100% MeOH [0.05% TFA], MS: EI+): retention time, 5.45
min; purity, 100%; [M + H]+: calcd, 228.14; found, 228.35 m/z.
HPLC (gradient 0-100% MeCN [0.05% TFA]): retention time,
3.84 min; purity, 100%.
O-(m,m-Dimethyl)benzyl-tyramine Hydrochloride (50). Refer
to the general procedure for t-Boc deprotection described above.
The crude reaction mixture was diluted with ether, and the
precipitate was collected by vacuum filtration to give 50 as a white
1
solid (28.6 mg, 86% yield). H NMR (400 MHz, DMOS-d6): δ
7.97 (br s, 3 H), 7.17 (d, J ) 8.4 Hz, 2 H), 7.03 (s, 2 H), 6.96
(ovrlp d, J ) 8.4 Hz, 2 H), 6.95 (ovrlp s, 1 H), 4.99 (s, 2 H), 2.97
(br s, 2 H), 2.81 (app t, J ) 8.0 Hz, 2 H), 2.27 (s, 6 H). HRMS
(EI+, free base) m/z for C17H21NO: calcd, 255.1623; found,
255.1633. LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 6.02 min; purity, 100%; [M + H]+:
calcd, 256.17; found, 256.56 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 4.43 min; purity, 100%.

1110 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3
Hart et al.
O-(m-Methoxy)benzyl-tyramine Hydrochloide (51). Refer to
the general procedure for t-Boc deprotection described above. The
crude reaction mixture was diluted with ether, and the precipitate
was collected by vacuum filtration to give 51 as a white solid (67.0
(app t, J ) 7.6 Hz, 2 H). HRMS (EI+, free base) m/z for C15H12F5-
NO: calcd, 317.0839; found, 317.0843. LC/MS (LC: gradient
0-100% MeOH [0.05% TFA], MS: EI+): retention time, 5.87
min; purity, 100%; [M - NH2 + H]+: calcd, 302.07; found, 302.50
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 4.28 min; purity, 100%.
N-Methyl-O-benzyl-tyramine Hydrochloride (62). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was concentrated in vacuo to give 62, which was
dried under high vacuum (118 mg, 89% yield). 1H NMR (400 MHz,
DMSO-d6): δ 8.90 (br s, 1H), 7.45-7.32 (m, 5 H), 7.18 (d, J )
8.4 Hz, 2 H), 6.75 (d, J ) 8.4 Hz, 2 H), 5.08 (s, 2H), 3.33 (s, 1H)
3.05 (br s, 2H) 2.86 (t, J ) 8.8 Hz, 2H) 2.54 (s, 3H). HRMS (EI+,
free base) m/z for C16H19NO [M + H]+: calcd, 242.1547; found,
242.1549. LC/MS (LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 5.42 min; purity, 100%; [M + H]+:
calcd, 242.15; found, 242.49 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 3.94 min; purity, 100%.
1
mg, 97% yield). H NMR (400 MHz, DMSO-d6): δ 7.87 (br s, 3
H), 7.30 (t, J ) 8.0 Hz, 1 H), 7.17 (d, J ) 8.4 Hz, 2 H), 6.94-7.20
(m, 4 H), 6.88 (app d, J ) 7.2 Hz, 1 H), 5.06 (s, 2 H), 3.75 (s, 3
H), 2.98 (br s, 2 H), 2.79 (app t, J ) 7.8 Hz, 2 H). HRMS (EI+,
free base) m/z for C16H19NO2: calcd, 257.1416; found: 257.1416.
LC/MS (LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+):
retention time, 5.45 min; purity, 100%; [M + H]+: calcd, 258.15;
found, 258.55 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 3.87 min; purity, 100%.
O-(m,m-Dimethoxy)benzyl-tyramine Hydrochloride (52). Re-
fer to the general procedure for t-Boc deprotection outlined above.
The precipitate was filtered to give 52 as a white solid (136 mg,
1
97% yield). H NMR (400 MHz, DMSO-d6): δ 7.89 (br s, 3 H),
7.17 (d, J ) 8.4 Hz, 2 H), 6.96 (d, J ) 8.8 Hz, 2 H), 6.58 (d, J )
1.6 Hz, 2 H), 6.44 (d, J ) 1.6 Hz, 1 H), 5.02 (s, 2 H), 3.73 (s, 6
H), 2.98 (app t, J ) 7.8 Hz, 2 H), 2.79 (app t, J ) 7.8 Hz, 2 H).
HRMS (EI+, free base) m/z for C17H21NO3: calcd, 287.1521; found,
287.1522. LC/MS(LC: gradient 0-100% MeOH [0.05% TFA],
MS: EI+): retention time, 5.52 min; purity, 100%; [M + H]+:
calcd, 288.16; found, 288.55 m/z. HPLC (gradient 0-100% MeCN
[0.05% TFA]): retention time, 3.97 min; purity, 100%.
N-Ethyl-O-benzyl-tyramine Hydrochloride (63). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the white precipitate
was collected by vacuum filtration to give 63 as a white solid (38.9
1
mg, 92% yield). H NMR (400 MHz, DMSO-d6): δ 8.70 (br s, 2
H), 7.45-7.30 (m, 5 H), 7.18 (d, J ) 8.4 Hz, 2 H), 6.97 (d, J )
8.4 Hz, 2 H), 5.09 (s, 2 H), 3.08 (app t, J ) 7.6 Hz, 2 H), 2.95 (q,
J ) 7.2 Hz, 2 H), 2.85 (app t, J ) 8.2 Hz, 2 H), 1.19 (t, J ) 7.2
Hz, 3 H). HRMS (EI+, free base) m/z for C17H21NO: calcd,
255.1623; found, 255.1616. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.50 min; purity, 100%;
[M + H]+: calcd, 256.17; found, 256.56 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 4.03 min; purity,
100%.
O-(p-Fluoro)benzyl-tyramine Hydrochloride (53). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the precipitate was
collected by vacuum filtration to give 53 as a white solid (50.4
1
mg, 90% yield). H NMR (400 MHz, DMSO-d6): δ 7.93 (br s, 3
H), 7.45 (app dd, J ) 8.4, 5.6 Hz, 2 H), 7.22 (ovrlp app t, J ) 8.8
Hz, 2 H), 7.18 (d, J ) 8.8 Hz, 2 H), 6.97 (d, J ) 8.8 Hz, 2 H),
5.07 (s, 2 H), 2.98 (app t, J ) 7.8 Hz, 2 H), 2.80 (app t, J ) 8.0
Hz, 2 H). HRMS (EI+, free base) m/z for C15H16HNO: calcd,
245.1216; found, 245.1214. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.50 min; purity, 100%;
[M + H]+: calcd, 246.13; found, 246.45 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 3.92 min; purity,
99%.
N-Propyl-O-benzyl-tyramine Hydrochloride (64). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the white precipitate
was collected by vacuum filtration to give 64 as a white solid (35.9
1
mg, 88% yield). H NMR (400 MHz, DMSO-d6): δ 8.72 (br s, 2
H), 7.45-7.30 (m, 5 H), 7.17 (d, J ) 8.4 Hz, 2 H), 6.98 (d, J )
8.8 Hz, 2 H), 5.09 (s, 2 H), 308 (app t, J ) 8.2 Hz, 2 H), 2.89-
2.84 (m, 4 H), 1.62 (sextet, J ) 7.5 Hz, 2 H), 0.91 (t, J ) 7.6 Hz,
3 H). HRMS (EI+, free base) m/z for C18H23NO: calcd, 269.1780;
found, 269.1771. LC/MS (LC: gradient 0-100% MeOH [0.05%
TFA], MS: EI+): retention time, 5.62 min; purity, 100%; [M +
H]+: calcd, 270.19; found, 270.58 m/z. HPLC (gradient 0-100%
MeCN [0.05% TFA]): retention time, 4.19 min; purity, 100%.
O-(p-Nitro)benzyl-tyramine Hydrocloride (54). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the precipitate was
collected by vacuum filtration to give 54 as a white solid (59.1
1
mg, 99% yield). H NMR (400 MHz, DMSO-d6): δ 8.26 (d, J )
8.8 Hz, 2 H), 7.95 (br s, 3 H), 7.71 (d, J ) 8.8 Hz, 2 H), 7.21 (d,
J ) 8.4 Hz, 2 H), 6.99 (d, J ) 8.4 Hz, 2 H), 5.27 (s, 2 H), 3.01-
2.95 (m, 2 H), 2.81 (app t, J ) 8.0 Hz, 2 H). HRMS (EI+, free
base) m/z for C15H16N2O3: calcd, 272.1161; found, 272.1163. LC/
MS (LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+):
retention time, 5.42 min; purity, 100%; [M - NH2 + H]+: calcd,
257.10; found, 257.46 m/z. HPLC (gradient 0-100% MeCN [0.05%
TFA]): retention time, 3.95 min; purity, 100%.
N-Butyl-O-benzyl-tyramine Hydrochloride (65). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the white precipitate
was collected by vacuum filtration to give 65 as a white solid (32.1
1
mg, 91% yield). H NMR (400 MHz, DMSO-d6): δ 8.71 (br s, 2
H), 7.45-7.30 (m, 5 H), 7.17 (d, J ) 8.8 Hz, 2 H), 6.98 (d, J )
8.8 Hz, 2 H), 5.09 (s, 2 H), 3.08 (app t, J ) 8.2 Hz, 2 H), 2.92-
2.84 (m, 4 H), 1.58 (quintet, J ) 7.7 Hz, 2 H), 1.33 (sextet, J )
7.4 Hz, 2 H), 0.89 (t, J ) 7.2 Hz, 3 H). HRMS (EI+, free base)
m/z for C19H25NO [M + H]+: calcd, 284.2014; found, 284.2015.
LC/MS (LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+):
retention time, 5.78 min; purity, 100%; [M + H]+: calcd, 284.20;
found, 284.59 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.39 min; purity, 100%.
O-(p-Trifluoromethyl)benzyl-tyramine Hydrochloride (55).
Refer to the general procedure for t-Boc deprotection described
above. The crude reaction mixture was diluted with ether, and the
precipitate was collected by vacuum filtration to give 55 as a white
1
solid (37.3 mg, 84% yield). H NMR (400 MHz, DMSO-d6): δ
7.90 (s, 3 H), 7.77 (d, J ) 8.4 Hz, 2 H), 7.66 (d, J ) 8.0 Hz, 2 H),
7.19 (d, J ) 8.8 Hz, 2 H), 6.99 (d, J ) 8.4 Hz, 2 H), 5.22 (s, 2 H),
2.99 (app t, J ) 8.0 Hz, 2 H), 2.80 (app t, J ) 7.8 Hz, 2 H). LC/
MS (LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+):
retention time, 5.97 min; purity, 100%; [M - NH2 + H]+: calcd,
280.11; found, 280.49 m/z. HPLC (gradient 0-100% MeCN [0.05%
TFA]): retention time, 4.41 min; purity, 100%.
N,O-Dibenzyl-tyramine Hydrochloride (66). Refer to the
general procedure for t-Boc deprotection described above. The crude
reaction mixture was diluted with ether, and the white precipitate
was collected by vacuum filtration to give 66 as a white solid (66.2
1
O-(2′,3′,4′,5′,6′-Pentafluoro)benzyl-tyramine Hydrochloride
(56). Refer to the genereal procedure for t-Boc deprotection
described above. The crude reaction mixture was diluted with ether,
and the precipitate was collected by vacuum filtration to give 56
white crystalline solid (72.7 mg, 95% yield). 1H NMR (400 MHz,
DMSO-d6): δ 7.82 (br s, 3 H), 7.19 (d, J ) 8.4 Hz, 2 H), 6.99 (d,
J ) 8.4 Hz, 2 H), 5.15 (s, 2 H), 2.98 (app t, J ) 7.6 Hz, 2 H), 2.79
mg, 85% yield). H NMR (400 MHz, DMSO-d6): δ 9.21 (br s, 2
H), 7.56-7.30 (m, 10 H), 7.16 (d, J ) 8.4 Hz, 2 H), 6.97 (d, J )
8.4 Hz, 2 H), 5.08 (s, 2 H), 4.16 (br s, 2 H), 3.09 (br s, 2 H), 2.91
(app t, J ) 8.2, 2 H). HRMS (EI+, free base) m/z for C22H23NO:
calcd, 317.1780; found, 317.1780. LC/MS (LC: gradient 0-100%
MeOH [0.05% TFA], MS: EI+): retention time, 5.93 min; purity,
100%; [M + H]+: calcd, 318.19; found, 318.63 m/z. HPLC

Synthetic Trace Amine Receptor Agonists
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3 1111
(gradient 0-100% MeCN [0.05% TFA]): retention time, 4.51 min;
purity, 100%.
precipitate was collected by filtration to give 83 as a white solid
(94.9 mg, 93% yield). 1H NMR (400 MHz, DMSO-d6): δ 7.94 (br
s, 3 H), 7.75 (d, J ) 8.0 Hz, 2 H), 6.67 (ovrlp d, J ) 1.6 Hz, 1 H),
7.66 (ovrlp d, J ) 8.0 Hz, 2 H), 7.21 (dd, J ) 2.0 Hz, 1 H), 6.99
(d, J ) 8.4 Hz, 1 H), 5.26 (s, 2 H), 2.95 (app t, J ) 7.8 Hz, 2 H),
2.78 (app t, J ) 7.6 Hz, 2 H). HRMS (EI+, free base) m/z for
C16H15F3INO: calcd, 421.0150; found, 421.0136. LC/MS (LC:
gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention time,
6.33 min; purity, 100%; [M + H]+: calcd, 422.02; found, 422.47
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 4.78 min; purity, 100%.
N,N-Dimethyl-O-benzyl-tyramine Hydrochloride (67). O-
Benzyl tyramine hydrochloride 38 (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 and concentrated to give the free amine. A solution of free
amine (0.22 mmol) in formic acid (>1.10 mmol, 88% in water
solution) and formaldehyde (>1.10 mmol, 37% in water solution)
was stirred at 80 °C for ∼20 h. After it was cooled to room
temperature, the reaction was diluted with water, adjusted to pH ∼
10 with K2CO3, and extracted with dichloromethane. The organic
layer was washed with brine, dried over MgSO4, and concentrated
to give the crude product. The crude mixture was treated with 3 N
anhydrous HCl/ethyl acetate (1 mL), exposed to diethyl ether, and
filtered to give 67 as a white solid (84.6 mg, 60% yield). 1H NMR
(400 MHz, DMSO-d6): δ 10.46 (br s, 1 H), 7.42-7.26 (m, 5 H),
7.15 (app d, J ) 8.4 Hz, 2 H), 6.94 (app d, J ) 8.8 Hz, 2 H),
3.21-3.13 (m, 2 H), 2.93-2.86 (m, 2 H), 2.73 (d, J ) 4.0 Hz, 6
H). HRMS (EI+, free base) m/z for C17H21NO: calcd, 255.1623;
found, 255.1617. LC/MS (LC: gradient 0-100% MeOH [0.05%
TFA], MS: EI+): retention time, 5.38 min; purity, 100%; [M +
H]+: calcd, 256.17; found, 256.56 m/z. HPLC (gradient 0-100%
MeCN [0.05% TFA]): retention time, 4.05 min; purity, 95%.
2-[3-Iodo-4-(p-hydroxy)phenoxyphenyl]ethanol (72). Refer to
the general procedure for silyl deprotection described above. The
crude product was purified via flash SiO2 [eluted with hexane/ethyl
N-Methyl-O-benzyl-3-iodotyramine Hydrochloride (84). Refer
to the general procedure for t-Boc deprotection described above.
The crude reaction mixture was diluted with ether, and the white
precipitate was collected by vacuum filtration to give 84 as a white
1
solid (35.9 mg, 91% yield). H NMR (400 MHz, DMSO-d6): δ
8.64 (br s, 2 H), 7.71 (d, J ) 2.0 Hz, 1 H), 7.49 (d, J ) 7.2 Hz, 2
H), 7.41 (app t, J ) 7.3 Hz, 2 H), 7.33 (app t, J ) 7.4 Hz, 1 H),
7.24 (dd, J ) 8.2, 2.2 Hz, 1 H), 7.05 (d, J ) 8.4 Hz, 1 H), 5.18 (s,
2 H), 3.10 (br s, 2 H), 2.83 (app t, J ) 7.8 Hz, 2 H), 2.55 (br s, 3
H). HRMS (EI+, free base) m/z for C16H18INO [M + H]+: calcd,
368.0513; found, 368.0509. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.88 min; purity, 100%;
[M + H]+: calcd, 368.05; found, 368.47 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 4.44 min; purity,
100%.
N-Methyl-O-(p-trifluoromethyl)benzyl-tyramine Hydrochlo-
ride (85). Refer to the general procedure for t-Boc deprotection
described above. The precipitate was filtered to give 85 as a white
1
acetate (2:1)] to give 72 as a white solid (35 mg, 85% yield). H
NMR (400 MHz, chloroform-d): δ 7.71 (d, J ) 2.4 Hz, 1 H),
7.09 (dd, J ) 2.4, 8.8 Hz, 1 H), 6.87 (d, J ) 9.2 Hz, 2 H), 6.79 (d,
J ) 9.2 Hz, 2 H), 6.70 (d, J ) 8.8 Hz, 1 H), 5.58 (br s, 1H), 3.85
1
solid (93.4 mg, 88% yield). H NMR (400 MHz, chloroform-d):
δ 8.77 (br s, 2 H), 7.76 (d, J ) 8.4 Hz, 2 H), 7.66 (d, J ) 7.6 Hz,
2 H), 7.19 (d, J ) 8.8 Hz, 2 H), 6.99 (d, J ) 8.8 Hz, 2 H), 5.22 (s,
2 H), 3.08 (br s, 2 H), 2.86 (app br t, J ) 8.0, 2 H), 2.55 (ovrlp br
s, 3 H). HRMS (EI+, free base) m/z for C17H18F3NO: calcd,
309.1340; found, 309.1331. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.97 min; purity, 100%;
[M + H]+: calcd, 310.14; found, 310.63 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 4.54 min; purity,
100%.
(t, J ) 6.4 Hz, 2 H), 2.80 (t, J ) 6.8 Hz, 2 H), 1.69 (br s, 1H). 13
C
NMR (100 MHz, chloroform-d): δ 156.2, 152.0, 150.2, 140.1,
135.1, 130.2, 120.2, 117.5, 116.1, 88.0, 63.5, 37.8. HRMS (EI+)
m/z for C14H13IO3: calcd, 355.9909; found, 355.9906. LC/MS
(LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention
time, 6.28 min; purity, 100%; [M - H + K]+: calcd, 393.95; found,
393.43 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.49 min; purity, 99%.
3-Methyl-thyronamine (77). Thyronamine derivative 76 (160
mg, 0.41 mmol) was dissolved in 3 N HCl solution in ethyl acetate
(2 mL, anhydrous), and the reaction mixture was stirred at ambient
temperature overnight. The crude mixture was concentrated in vacuo
and dried under high vacuum pressure to give the pure product 77
as a white solid (110 mg, 96% yield). 1H NMR (400 MHz, DMSO-
d6): δ 9.27 (br, 1 H), 7.94 (br, 2 H), 7.16 (s, 1 H), 7.02 (d, J ) 8.4
Hz, 1 H), 6.76 (m, 3 H), 6.67 (d, J ) 8.2 Hz, 2 H), 3.01 (m, 2 H),
2.81 (m, 2 H), 2.19 (s, 3 H). 13C NMR (100 MHz, methanol-d4): δ
156.7, 154.3, 151.3, 132.6, 132.1, 130.3, 128.3, 120.5, 118.9, 117.1,
42.1, 33.8, 16.3. HRMS (EI+, free base) m/z for C15H17NO2: calcd,
243.1259; found, 243.1296. LC/MS (LC: gradient 0-100% MeOH
[0.05% TFA], MS: EI+): retention time, 5.08 min; purity, 100%;
[M - NH2]+: calcd, 227.11; found, 227.45 m/z. HPLC (gradient
0-100% MeCN [0.05% TFA]): retention time, 3.52 min; purity,
95%.
O-Phenyl-3-iodotyramine Hydrochloride (91). Refer to the
general procedure for t-Boc deprotection described above. The
precipitate was collected by filtration to give 91 as a white solid
(250 mg, 88% yield). 1H NMR (400 MHz, DMSO-d6): δ 7.92 (br
s, 3 H), 7.80 (d, J ) 2.0 Hz, 1 H), 7.33 (app t, J ) 8.0 Hz, 2 H),
7.27 (dd, J ) 8.2, 2.2 Hz, 1 H), 7.08 (t, J ) 7.4 Hz, 1 H), 6.91 (d,
J ) 8.8 Hz, 1 H), 6.87 (app d, J ) 8.6 Hz, 2 H), 3.07-2.97 (m, 2
H), 2.83 (app t, J ) 7.8 Hz, 2 H). HRMS (EI+, free base) m/z for
C14H14INO: calcd, 339.0120; found, 399.0128. LC/MS (LC:
gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention time,
5.78 min; purity, 100%; [M + H]+: calcd, 340.02; found, 340.45
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 4.20 min; purity, 100%.
O-(p-Fluoro)phenyl-3-iodotyramine Hydrochloride (92). Refer
to the general procedure for t-Boc deprotection above. The reaction
was concentrated to dryness and dried in vacuo to give 92 as a
slightly yellow residue (43.6 mg, 97% yield). 1H NMR (400 MHz,
DMSO-d6): δ 8.72 (br s, 2 H), 7.79 (d, J ) 0.8 Hz, 1 H), 7.25
(dd, J ) 8.4, 1.2 Hz, 1 H), 7.17 (app t, J ) 8.8 Hz, 2 H), 6.94-
6.87 (m, 3 H), 3.08 (app t, J ) 8.0 Hz, 2 H), 2.86 (app t, J ) 7.8
Hz, 2 H), 2.51 (s, 3 H). HRMS (EI+, free base) m/z for C15H15-
FICO: calcd, 371.0182; found, 371.0178. LC/MS (LC: gradient
0-100% MeOH [0.05% TFA], MS: EI+): retention time, 5.87
min; purity, 100%; [M + H]+: calcd, 372.03; found, 372.50 m/z.
HPLC (gradient 0-100% MeCN [0.05% TFA]): retention time,
4.37 min; purity, 98%.
O-Benzyl-3-iodotyramine Hydrochloride (82). Refer to the
general procedure for the t-Boc deprotection described above. The
crude reaction mixture was diluted with ether, and the white
precipitate was collected by vacuum filtration to give 82 as a white
1
solid (18.6 mg, 88% yield). H NMR (400 MHz, DMSO-d6): δ
7.90 (br s, 3 H), 7.69 (d, J ) 2.0 Hz, 1 H), 7.48 (d, J ) 7.2 Hz, 2
H), 7.40 (t, J ) 7.4 Hz, 2 H), 7.32 (app t, J ) 7.2 Hz, 1 H), 7.23
(dd, J ) 8.4, 2.0 Hz, 1 H), 7.03 (d, J ) 8.8 Hz, 1 H), 5.17 (s, 2 H),
2.99 (br s, 2 H), 2.78 (t, J ) 7.8 Hz, 2 H). HRMS (EI+, free base)
m/z for C15H16INO: calcd, 353.0277; found, 353.0280. LC/MS
(LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention
time, 5.90 min; purity, 100%; [M + H]+: calcd, 354.04; found,
354.46 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.31 min; purity, 100%.
O-(p-trifluromethyl)phenyl-3-iodotyramine (93). Refer to the
general procedure for t-Boc deprotection above. The reaction was
concentrated to dryness and dried in vacuo to give 93 as a slightly
yellow residue (34.5 mg, 97% yield). 1H NMR (400 MHz, DMSO-
d6): δ 8.86 (br s, 2 H), 7.85 (s, 1 H), 7.68 (d, J ) 8.4 Hz, 2 H),
7.34 (app d, J ) 8.0 Hz, 1 H), 7.13 (d, J ) 8.0 Hz, 1 H), 6.99 (d,
O-(p-trifluoromethyl)benzyl-3-iodotyramine Hydrochloride
(83). Refer to the general procedure for t-Boc deprotection. The

1112 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 3
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J ) 8.8 Hz, 2 H), 3.12 (t, J ) 7.6 Hz, 2 H), 2.92 (t, J ) 7.6 Hz,
2 H), 2.52 (s, 3 H). HRMS (EI+, free base) m/z for C16H15F3INO
[M + H]+: calcd, 422.0229; found, 422.0222. LC/MS (LC:
gradient 0-100% MeOH [0.05% TFA], MS: EI+): retention time,
6.20 min; purity, 100%; [M + H]+: calcd, 422.02; found, 422.47
m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]): retention
time, 4.76 min; purity, 98%.
N-Methyl-3-iodothyronamine Hydrochoride (96). Refer to the
general procedures for silyl deprotection and t-Boc deprotection
described above. The crude deprotected product was submitted to
t-Boc deprotection conditions without further purification. The
precipitate was filtered to give 96 as a white solid (7.7 mg, 60%
1
yield for both steps). H NMR (400 MHz, DMSO-d6): δ 9.39 (s,
1 H), 8.57 (br s, 2 H), 7.78 (d, J ) 2.4 Hz, 1 H), 7.21 (dd, J ) 8.8,
2.4 Hz, 1 H), 6.82 (app dt, J ) 9.2, 2.8 Hz, 2 H), 6.78 (app dt, J
) 9.2, 2.8 Hz, 2 H), 6.71 (d, J ) 8.2 Hz, 1 H), 3.12 (app br d, J
) 6.0 Hz, 2 H), 2.86 (app br t, J ) 7.8 Hz, 2 H), 2.56 (br s, 3 H).
HRMS (EI+, free base) m/z for C15H16INO2 [M - NHCH3 + H]+:
calcd, 339.9960; found, 339.9941. LC/MS (LC: gradient 0-100%
MeOH [0.05% TFA], MS: EI+): retention time, 5.28 min; purity,
100%; [M + H]+: calcd, 370.03; found, 370.46 m/z. HPLC
(gradient 0-100% MeCN [0.05% TFA]): retention time, 3.76 min;
purity, 100%.
N,O-Dimethyl-3-iodothyronamine Hydrochloride (97). Refer
to the general procedure for t-Boc deprotection described above.
The precipitate was filtered to give 97 as a white solid (34.9 mg,
1
89% yield). H NMR (400 MHz, DMSO-d6): δ 8,82 (br s, 2 H),
7.80 (d, J ) 2.0 Hz), 7.25 (dd, J ) 8.4, 2.0 Hz, 1 H), 6.95 (app dt,
J ) 9.2, 2.6 Hz, 2 H) 6.91 (app dt, J ) 9.2, 2.6 Hz, 2 H), 6.78 (d,
J ) 8.4 Hz, 1 H), 3.74 (s, 3 H), 3.16-3.08 (br m, 2 H), 2.89 (app
t, J ) 7,8 Hz, 2 H), 2.57-2.53 (br m, 3 H). HRMS (EI+, free
base) m/z for C16H18INO2: calcd, 383.0382; found, 383.0391. LC/
MS (LC: gradient 0-100% MeOH [0.05% TFA], MS: EI+):
retention time, 5.80 min; purity, 100%; [M + H]+: calcd, 384.05;
found, 384.47 m/z. HPLC (gradient 0-100% MeCN [0.05% TFA]):
retention time, 4.24 min; purity, 99%.
Acknowledgment. This research was supported by grants
from the National Institutes of Health (Grant DK52798 to T.S.S.)
and by the Sandler Family Supporting Foundation (to T.S.S.).
Supporting Information Available: Experimental procedures
for all intermediates and LC/MS and HPLC data for final
compounds. This material is available free of charge via the Internet
at http://pubs.acs.org.
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