Synthesis and biological evaluation of a series of liver-selective phosphonic acid thyroid hormone receptor agonists and their prodrugs

Article abstract of DOI:10.1021/jm800824d

Phosphonic acid (PA) thyroid hormone receptor (TR) agonists were synthesized to exploit the poor distribution of PA-based drugs to extrahepatic tissues and thereby to improve the therapeutic index. Nine PAs showed excellent TR binding affinities (TRβ

Full text of DOI:10.1021/jm800824d

J. Med. Chem. 2008, 51, 7075–7093
7075
Synthesis and Biological Evaluation of a Series of Liver-Selective Phosphonic Acid Thyroid
Hormone Receptor Agonists and Their Prodrugs
Serge H. Boyer,*,† Hongjian Jiang,† Jason D. Jacintho,† Mali Venkat Reddy,† Haiqing Li,† Wenyu Li,† Jennifer L. Godwin,†
William G. Schulz,† Edward E. Cable,‡ Jinzhao Hou,‡ Rongrong Wu,‡ James M. Fujitaki,‡ Scott J. Hecker,† and
Mark D. Erion†,‡
Departments of Medicinal Chemistry and Biosciences, Metabasis Therapeutics, Inc., 11119 North Torrey Pines Road,
La Jolla, California 92037
ReceiVed March 16, 2008
Phosphonic acid (PA) thyroid hormone receptor (TR) agonists were synthesized to exploit the poor distribution
of PA-based drugs to extrahepatic tissues and thereby to improve the therapeutic index. Nine PAs showed
excellent TR binding affinities (TRꢀ1, Ki < 10 nM), and most of them demonstrated significant cholesterol
lowering effects in a cholesterol-fed rat (CFR) model. Unlike the corresponding carboxylic acid analogue
and T3, PA 22c demonstrated liver-selective effects by inducing maximal mitochondrial glycerol-3-phosphate
dehydrogenase activity in rat liver while having no effect in the heart. Because of the low oral bioavailability
of PA 22c, a series of prodrugs was synthesized and screened for oral efficacy in the CFR assay. The
liver-activated cyclic 1-(3-chlorophenyl)-1,3-propanyl prodrug (MB07811) showed potent lipid lowering
activity in the CFR (ED50 0.4 mg/kg, po) and good oral bioavailability (40%, rat) and was selected for
development for the treatment of hypercholesterolemia.
Chart 1. Structures of TR Ligands
Introduction
Dyslipidemia is a key contributor to coronary heart disease
(CHDa),1 the leading cause of death in the U.S.,2 and is a
growing epidemic in developed countries. A major contributor
to dyslipidemia is hypercholesterolemia, which is usually
attributed to high levels of low-density lipoprotein cholesterol
(LDL-C) and regarded by the National Cholesterol Education
Program (NCEP) as an important risk factor.3 Currently,
therapies such as hydroxymethylglutaryl coenzyme A (HMG-
CoA) reductase inhibitors (statins4) and agents that limit
cholesterol absorption (e.g., ezetimibe,5 bile acid sequestrants6)
are used alone or in combination to help patients achieve the
NCEP-recommended LDL-C level. While large scale clinical
trials with statins have established that every 1% lowering of
LDL-C resulted in an approximate 1% reduction in CHD risk,7
many patients on statin therapy still fail to bring their LDL-C
within the normal range,8 necessitating the discovery of ad-
ditional therapies having additive effects with statins.
The thyroid hormones (THs) play a critical role in growth,
development, metabolism, and homeostasis.9 They are produced
by the thyroid gland as thyroxine (T4, 1a, Chart 1) and 3,5,3′-
triiodo-L-thyronine (T3, 1b, Chart 1). T4 is the major secreted
form in humans and is enzymatically deiodinated by deiodinases
to the more active form, T3, in peripheral tissues. THs exert
their action by interacting with thyroid hormone receptors (TRs),
which belong to the nuclear hormone receptor superfamily, and
regulate the transcription of target genes.10 TRs are expressed
in most tissues and exist as two isoforms (TRR and TRꢀ) that
are expressed predominantly as the alternatively spliced variants
TRR1 and TRꢀ1. Tissue distribution studies,9 mouse knockout
studies,11 and evaluation of patients with resistance to thyroid
hormone (RTH) syndrome12 have established that TRR1 is the
predominant isoform in the heart and regulates most cardiac
functions, while the TRꢀ1 isoform predominates in the liver and
the pituitary and regulates cholesterol metabolism and thyroid-
stimulating hormone (TSH) production, respectively.
In recognition of the potential benefits associated with
modulation of TRs, numerous approaches have been pursued
to identify a suitable TR agonist. Initial studies with T3 and T4
in humans demonstrated their usefulness in lowering plasma
cholesterol levels.13 However, these benefits were offset by
deleterious cardiovascular side effects (tachycardia, arrhyth-
mia).14 Consequently, more recent approaches focused on the
identification of TR agonists that bind preferentially to the
TRꢀ1.15 N-[3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylphenox-
y)phenyl]oxamic acid (CGS 23425, 2) showed preferential
* To whom correspondence should be addressed. Phone: 858-622-5576.
Fax: 858-622-5573. E-mail: boyer@mbasis.com.
†
Department of Medicinal Chemistry.
Department of Biosciences.
‡
a Abbreviations: CHD, coronary heart disease; LDL-C, low-density
lipoprotein cholesterol; NCEP, National Cholesterol Education Program;
HMG-CoA, hydroxymethylglutaryl coenzyme A; TH, thyroid hormone; T4,
thyroxine or 3,5,3′,5′-tetraiiodo-L-thyronine; T3, 3,5,3′-triiodo-L-thyronine;
TR, thyroid hormone receptor; RTH, resistance to thyroid hormone; TSH,
thyroid-stimulating hormone; TI, therapeutic index; PA, phosphonic acid;
TPC, total plasma cholesterol; mGPDH, mitochondrial glycerol-3-phosphate
dehydrogenase; TRIAC, 3,5-diiodo-4-(4′-hydroxy-3′-iodophenoxy)pheny-
lacetic acid; HPT, hypothalamic-pituitary-thyroid.
10.1021/jm800824d CCC: $40.75
2008 American Chemical Society
Published on Web 11/01/2008

7076 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
Scheme 1a
a Reagents and conditions: (a) (1) P(OEt)3, THF; (2) NH2OH, pyridine, room temp, 85% for two steps; (b) NaBH4, NiCl2, MeOH, room temp; (c)
(Boc)2O, THF, room temp, 46% for two steps; (d) H2, Pd-C, MeOH; (e) I(Py)2BF4, CH2Cl2, 0 °C to room temp, 88% for two steps; (f)
4-(tert-butyldimethylsilyloxy)phenylboronic acid, Cu(OAc)2, Et3N, CH2Cl2, room temp, 60%; (g) TBAF, THF, room temp, 62%; (h) 70% aqueous TFA,
room temp; (i) I2, KI, MeNH2, EtOH, 0 °C, 69% for two steps; (j) TMSBr, CH2Cl2, -30 °C to room temp, 95%.
binding to the rat liver nuclear TR over plasma membrane TR16
and was later found to be a TRꢀ1-selective TR agonist.17
Compound 2 demonstrated good lipid lowering effects in
hypercholesterolemic rats without cardiac side effects.17 Scan-
lan’s group identified 3,5-dimethyl-4-(4′-hydroxy-3′-isopropy-
lbenzyl)phenoxyacetic acid (GC-1, 3) and showed it to be 10
times more selective toward human TRꢀ1 than TRR1.18 TR
agonist 3 exhibited a rightward shift (20-fold) of the dose
response for heart rate compared to the dose response for
cholesterol lowering in hypercholesterolemic rats.19 In addition,
3 shows a higher level of uptake in the liver versus heart that
may further contribute to the cardiac sparing effect observed in
vivo.20 In 2003, 3,5-dichloro-4-(4′-hydroxy-3′-isopropylphe-
noxy)phenylacetic acid (KB-141, 4) was reported by Karo Bio
to have 14-fold higher affinity toward human TRꢀ1 than TRR1.21
In primate studies, TR agonists 4 lowered both plasma
cholesterol and body weight at doses that did not affect heart
rate.22 On the basis of these preclinical data, 323 and the recently
disclosed TR agonist [3,5-dibromo-4-(4′-hydroxy-3′-isopropy-
lphenoxy)phenylamino]-3-oxopropanoic acid (KB-2115, 5)24
were evaluated in humans, and both compounds lowered LDL-C
and were generally well tolerated. However, the long-term
effects of these carboxylic acids are unknown because the TRꢀ1-
selective agonists 320 and 422 do not show a separation between
cholesterol lowering vs thyroid stimulating hormone (TSH)
lowering, a process mediated by TRꢀ1 in the pituitary.10
In contrast to the traditional approach focusing on TRꢀ1-
selective ligands, our strategy revolved around developing TR
agonists that would selectively be transported into the liver and
consequently avoid TR activation in the pituitary or in the
heart.25Since TRꢀ1 is highly expressed in the liver,10 we
envisioned that liver-targeted TR agonists would retain lipid
lowering effects but would have fewer side effects in extrahe-
patic tissues than any of the synthetic TR agonists described to
date.18,21 Since phosphonic acids (PAs) are highly charged
molecules at physiological pH and usually have limited tissue
distribution outside the liver and kidney, where organic anion
transporters are highly expressed,26 we hypothesized that PA
ligands would achieve liver-specific TR activity if those
compounds could bind to human TR with sufficient affinity.
Moreover, their liver specificity could potentially be enhanced
by use of liver-targeting prodrugs developed in our laborato-
ries.27 Thus, we synthesized a series of PAs that incorporated
key structural elements considered important for TR binding
affinity and evaluated their structure-activity relationships with
respect to TR binding affinity, in vivo cholesterol lowering
efficacy, and TR agonist activity in the liver and heart. Results
from these studies led to the identification of the liver-selective
TR agonist 22c.
Unlike the carboxylic acid-containing TR agonists, 22c
exhibited low oral bioavailability in rats and monkeys based
on plasma levels. Consequently, we investigated a variety of
phosphonate prodrugs29 to assess their ability to enhance oral
bioavailability, including acyloxyalkyl esters,30 alkoxycarbo-
nyloxyalkyl esters,31 S-acylthioethyl esters,32 diphenyl esters,33
phosphonic diamides,34 and cyclic 1-(aryl)-1,3-propanyl (Hep-
Direct)27 prodrugs. To avoid activation of the prodrug in
extrahepatic tissues and the associated side effects, we searched
for either prodrugs that undergo rapid prodrug cleavage in the
plasma to 22c, which then selectively distributes to the liver,
or prodrugs with hepatocyte-specific cleavage to 22c. These
efforts led to the selection of the cyclic 1-(aryl)-1,3-propanyl
prodrug class, which is the only known prodrug class that
combines stability in extrahepatic tissue with selective activation
in hepatocytes, giving it liver-targeting capability.
The present report discloses the synthesis and SAR of a series
of phosphonic acid TR agonists, as well as an orally bioavailable
prodrug of 22c, 72 (MB07811), that shows potent oral efficacy
in the cholesterol-fed rat.
Chemistry
A series of phosphonic acids containing the structural
backbones of known carboxylic acid ligands were synthesized.
As described in Scheme 1, the T3 analogue was prepared from
commercially available 4-benzyloxyphenylacetyl chloride 6.
Michaelis-Arbuzov reaction35 with triethyl phosphite followed
by treatment of the resulting ketophosphonate with hydroxy-

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7077
Scheme 2a
a Reagents and conditions: (a) (1) diphosgene, dioxane, room temp to 60 °C; (2) HP(O)(OEt)2, Et3N, hexanes, room temp to 80 °C, 64% for two steps;
(b) TMSBr, CH2Cl2, -30 °C to room temp; (c) BBr3, CH2Cl2, -78 °C to room temp, 42% for two steps.
Scheme 3a
a Reagents and conditions: (a) n-BuLi, THF, -78 °C, 60-85%; (b) H2, Pd-C, AcOH-EtOAc, room temp; (c) TBAF, THF, 0 °C to room temp, 85%
for two steps; (d) TfOCH2P(O)(OEt)2, Cs2CO3 or TsOCH2P(O)(OEt)2, NaH, DMF, room temp, 60-80%; (e) TMSBr, CH2Cl2, -30 °C to room temp,
90-100%.
lamine generated oxime 7.36 Reduction with sodium borohydride
in the presence of nickel chloride37 followed by treatment with
di-tert-butyl dicarbonate gave 8, which was converted to phenol
9 by hydrogenolysis and iodination with bis(pyridine)iodonium
tetrafluoroborate. Coupling of 9 with 4-(tert-butyldimethylsi-
lyloxy)phenylboronic acid in the presence of copper acetate
afforded biaryl ether 10, which was deprotected to give phenol
11. Removal of the tert-butoxycarbonyl protecting group
followed by monoiodination with iodine and potassium iodide
yielded phosphonate 12. Deprotection with trimethylsilyl bro-
mide provided the T3 phosphonic acid analogue 13. The
phosphonic acid analogue of 3 was prepared from aniline 1416
(Scheme 2). Treatment of 14 with diphosgene followed by
diethyl phosphite provided phosphonate 15,38 which was depro-
tected as described above to give phosphonic acid 16.
As outlined in Scheme 3, phosphonic acids based on TR
agonist 3 (benzylphenyl series) were synthesized from the
triisopropylsilyl-protected benzaldehydes 17a,b and the
methoxymethyl-protected phenols 18a-e, both of which were
prepared from commercially available starting materials
according to the known procedures.39 Treatment of 18a-e
with n-butyllithium at -78 °C followed by coupling with
17a,b generated benzyl alcohols 19a-f, which were con-
verted to phenols 20a-f by hydrogenolysis and deprotection
with tetrabutylammonium fluoride. The phosphonate moiety
was introduced by alkylation of phenols 20a-f with diethyl
tosyloxymethylphosphonate (or diethyl trifluoromethylsul-
fonyloxymethylphosphonate) in the presence of cesium
carbonate or sodium hydride to provide phosphonates 21a-f
in 60-80% yield. Final deprotection of 21a-f with trim-
ethylsilyl bromide led to phosphonic acids 22a-f.
dibromoethane provided 25. Introduction of the phosphonate
by Michaelis-Arbuzov reaction generated 26, which was
deprotected with trimethylsilyl bromide to afford phosphonic
acid homologue 27. Also, treatment of 20c with triflic anhydride
yielded triflate 23, which underwent a Heck reaction with diethyl
vinylphosphonate in the presence of tetrakis(triphenylphos-
phine)palladium to give phosphonate 28. Hydrogenation fol-
lowed by deprotection with trimethylsilyl bromide led to
phosphonic acid 29. Alternatively, triflate 23 was converted to
methyl benzoate 24 by palladium-catalyzed carbonylation.
Treatment of 24 with sodium hydroxide followed by Curtius
rearrangement with diphenylphosphoryl azide in tert-butanol
generated the tert-butoxycarbonyl-protected aniline 30.41 In-
troduction of the phosphonate moiety with diethyl trifluorom-
ethylsulfonyloxymethylphosphonate yielded 31, which was
deprotected with hydrogen chloride and trimethylsilyl bromide
to provide phosphonic acid 32.
Phosphonic acids based on TR agonist 4 (diphenyl ether
series) were constructed from the appropriate phenols and bis(3-
isopropyl-4-methoxyphenyl)iodonium tetrafluoroborate 33 ac-
cording to the known methods.16,21 As shown in Scheme 5,
coupling of phenols 34a-c with 33 provided methyl benzoates
35a-c, which were converted to benzyl bromides 36a-c by
reduction with diisobutylaluminum hydride followed by treat-
ment of the resulting benzyl alcohols with carbon tetrabromide
and triphenylphosphine. 36a-c were reacted with triethyl
phosphite to provide phosphonates 37a-c, which were depro-
tected with trimethylsilyl bromide followed by boron tribromide
to afford phosphonic acids 38a-c. In addition, 36c (R1 ) Br)
was reacted with diethyl methylphosphonate to yield phospho-
nate 39,42 which was deprotected as described above to generate
phosphonic acid 40.
Previous studies in the field demonstrated the importance of
the linker between the carboxylic acid and the phenyl group on
the binding affinity.16,40 To explore this effect in the phosphonic
acid series, analogues 27, 29, and 32 were synthesized. As
described in Scheme 4, coupling of phenol 20c with 1,2-
The triiodo and diiodo analogues were prepared from benzyl
bromide 4143 as illustrated in Scheme 6. Benzyl bromide 41
underwent Michaelis-Arbuzov reaction with triethyl phosphite
followed by hydrogenolysis to give phenol 42, which was

7078 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
Scheme 4a
a Reagents and conditions: (a) Tf2O, DMAP, CH2Cl2, 0 °C, 100%; (b) CO (60 psi), Pd(OAc)2, 1,3-bis(diphenylphosphino)propane, Et3N, MeOH-DMF,
90 °C, 93%; (c) BrCH2CH2Br, Cs2CO3, DMF, 60 °C, 16%; (d) P(OEt)3, DMF, 140 °C, 50%; (e) TMSBr, CH2Cl2, -30 °C to room temp; (f) diethyl
vinylphosphonate, Pd(PPh3)4, DMF, 90 °C, 45%; (g) H2, Pd-C, MeOH, room temp, 100%; (h) NaOH, MeOH, 50 °C, 98%; (i) diphenylphosphoryl azide,
Et3N, tert-butanol, 80 °C, 75%; (j) TfOCH2P(O)(OEt)2, LDA, THF, 0 °C to room temp, 49%; (k) 2 N HCl, MeOH, room temp, 51%.
Scheme 5a
a Reagents and conditions: (a) Cu, Et3N, CH2Cl2, 0 °C to room temp, 80%; (b) DIBAL-H, THF, 0 °C; (c) CBr4, PPh3, Et2O, room temp, 54% for two
steps; (d) P(OEt)3, DMF, 120 °C, 85%; (e) TMSBr, CH2Cl2, -30 °C to room temp; (f) BBr3, CH2Cl2, -78 °C to room temp, 40-80% for two steps; (g)
CH3P(O)(OEt)2, THF, LDA, -78 °C to room temp, 43%.
converted to diiodophenol 43 upon treatment with bis(pyridi-
ne)iodonium tetrafluoroborate.44 Coupling with iodonium salt
33 yielded biaryl ether 44, which was deprotected with
trimethylsilyl bromide and boron tribromide to generate phos-
phonic acid 45. Also, 43 was reacted with 4-(tert-butyldimeth-
ylsilyloxy)phenylboronic acid in the presence of copper acetate
followed by deprotection with tetrabutylammonium fluoride to
provide phenol 46.45 Monoiodination of 46 with iodine and
potassium iodide led to 47, which was deprotected with
trimethylsilyl bromide to give the triiodo-substituted phosphonic
acid 48.
Several analogues with an oxygen-connected side chain were
prepared as outlined in Scheme 7. Coupling of 3,5-dimethyl-
4-hydroxylbenzaldehyde 49 with iodonium salt 33 gave ben-
zaldehyde 50, which was reacted with 3-chloroperoxybenzoic
acid followed by treatment with sodium hydroxide to provide
phenol 54c. Alternatively, either bromination or iodination of
commercially available phenol 51 gave the substituted phenols
52a,b. Coupling with iodonium salt 33 provided biaryl ethers
53a,b, which were converted to phenols 54a,b after alkaline
hydrolysis with sodium hydroxide. Deprotection of 54a-c with
boron tribromide gave diphenols 55a-c. Selective alkylation

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7079
Scheme 6a
a Reagents and conditions: (a) P(OEt)3, DMF, 120 °C; (b) H2, Pd-C, MeOH, room temp, 84% for two steps; (c) I(Py)2BF4, CH2Cl2, 0 °C to room temp,
90%; (d) 33, Cu, Et3N, CH2Cl2, 0 °C to room temp, 85%; (e) TMSBr, CH2Cl2, -30 °C to room temp, (f) BBr3, CH2Cl2, -78 °C to room temp, 92% for
two steps; (g) 4-(tert-butyldimethylsilyloxy)phenylboronic acid, Cu(OAc)2, CH2Cl2, room temp; (h) TBAF, THF, room temp, 13% for two steps; (i) I2, KI,
MeNH2, MeOH, 0 °C, 69%.
Scheme 7a
a Reagents and conditions: (a) Cu, 33, Et3N, CH2Cl2, 0 °C to room temp, 98-100%; (b) m-CPBA, room temp, 47%; (c) NaOH, MeOH, room temp, 95%;
(d) [CH3(CH2)3]4NBr3, CH2Cl2, room temp, 75% (for 52a) or I(Py)2BF4, CH2Cl2, 0 °C to room temp, 84% (for 52b); (e) BBr3, CH2Cl2, -78 °C to room
temp, 66%; (f) TfOCH2P(O)(OEt)2, Cs2CO3, DMF, room temp, 55%; (g) TMSBr, CH2Cl2, -30 °C to room temp, 63%.
with diethyl trifluoromethylsulfonyloxymethylphosphonate yielded
phosphonates 56a-c as the only products in 34-70% yield.
Final deprotection with trimethylsilyl bromide led to phosphonic
acids 57a-c.
N-chlorosuccinimide followed by Michaelis-Arbuzov reaction
with triethyl phosphite generated phosphonate 64.47 Deprotection
with tetrabutylammonium fluoride afforded phenol 65. Coupling
with iodonium salt 33 led to 66, which was converted to
phosphonic acid 67 by treatment with trimethylsilyl bromide
and boron tribromide.
Prodrugs of phosphonic acid TR agonist 22c were synthesized
in one step according to known procedures. Alkylation with
pivaloyloxymethyl iodide48 or alkoxycarbonyloxymethyl io-
dide33 provided the corresponding bis(pivaloyloxymethyl) (bis-
POM) (68, Scheme 10) and bis-alkoxycarbonyloxymethyl
prodrugs (69, 70) in good yield. Dicyclohexyldiimide-mediated
coupling of S-acetylthioethan-2-ol provided the corresponding
bis-S-acetylthioethyl prodrug (SATE, 71) in 56% yield. Use of
the same procedure with 1-aryl-1,3-propane diols49 provided
Two analogues with a nitrogen-connected side chain were
synthesized as described in Scheme 8. Treatment of com-
mercially available phenols 58a,b with di-tert-butyl dicarbonate
followed by coupling with iodonium salt 33 yielded biaryl ethers
59a,b. Alkylation with diethyl trifluoromethylsulfonyloxym-
ethylphosphonate gave phosphonates 60a,b, which were depro-
tected with trimethylsilyl bromide followed by boron tribromide
to provide phosphonic acids 61a,b. An analogue with a sulfur-
connected side chain was also prepared as outlined in Scheme
9. Treatment of 62 with n-butyllithium followed by dimethyl
disulfide gave thioanisole 63 in excellent yield.46 Treatment with

7080 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
Scheme 8a
a Reagents and conditions: (a) (Boc)2O, CH2Cl2, 93%; (b) 33, Et3N, Cu, CH2Cl2, 0 °C to room temp, 95%; (c) TfOCH2P(O)(OEt)2, NaH, THF, room
temp, 63-70%; (d) TMSBr, CH2Cl2, -30 °C to room temp; (e) BBr3, -78 °C to room temp, 85-91% for two steps.
Scheme 9a
a Reagents and conditions: (a) n-BuLi, Me2S2, THF, -78 °C to room temp, 100%; (b) NCS, CCl4, room temp; (c) P(OEt)3, 180 °C, 52% for two steps;
(d) TBAF, THF, room temp, 85%; (e) Cu, 33, Et3N, CH2Cl2, 0 °C to room temp, 60%; (f) TMSBr, CH2Cl2, -30 °C to room temp; (g) BBr3, CH2Cl2, -78
°C to room temp, 51% for two steps.
cis cyclic 1-(aryl)-1,3-propanyl prodrugs 72-78 in 20-40%
yield after removal of the undesired trans isomer by column
chromatography. Phosphonic diamide prodrugs were synthesized
by generating the phosphonyl dichloride with oxalyl chloride
followed by diamide formation with the corresponding amino
acid ethyl ester to give phosphonic diamides34 79-83 in
20-52% yield.
low binding affinity. This is probably due to the lack of the
necessary structural flexibility as observed in other TR ligands.52
Moreover, the length of the side chain (Y group) also had a
significant effect on binding potency. The binding affinity of
homologue 27 (Ki ) 87 nM) was 30-fold lower than that of
22c (Ki ) 2.95 nM). Replacement of oxygen between the phenyl
ring and the side chain with nitrogen (32, Ki ) 9.10 nM) or
methylene (29, Ki ) 31.3 nM) also decreased the binding
potency. Not surprisingly, low binding affinity was observed
for analogue 22f (R1 ) OMe, Ki ) 146 nM).
Results
Receptor Binding Affinity. All phosphonic acids described
above were tested in a receptor binding assay expressing human
TRR1 and TRꢀ1. The results are summarized in Table 1.
Unexpectedly, the phosphonic acid analogues 16 (TRꢀ1, Ki )
36.0 nM; unless otherwise specified, all following binding
affinities are for TRꢀ1) and 13 (Ki ) 271 nM) showed
considerably reduced binding activity when compared to their
corresponding carboxylic acids 2 (Ki ) 0.47 nM) and 1b (Ki )
0.68 nM), respectively. However, the phosphonic acid analogue
22c displayed potent binding affinity toward human TRꢀ1 (Ki
) 2.95 nM), though its activity was 9-fold weaker than that of
3 (Ki ) 0.32 nM). To explore the SAR in this series, we
synthesized several analogues with different moieties on the ring
and side chain. Among these compounds (X ) CH2, Y )
OCH2), the 3′-subsitutents (R2) had a major impact on the
binding potency. Consistent with previous reports for carboxylic
acid ligands,50,51 the binding affinity increased in the order of
methyl (22a), ethyl (22b), and isopropyl (22c) groups. The sec-
butyl group (22e) was also well tolerated at this position. As
expected, the 3′-phenyl analogue (22d, Ki ) 106 nM) showed
While analogue 38b (Ki ) 52.3 nM) only showed moderate
binding affinity, the 3,5-diiodo-substituted phosphonic acids 45
(X ) O, Y ) CH2, Ki ) 0.84 nM) and 57b (X ) O, Y )
OCH2, Ki ) 0.97 nM) displayed excellent binding potency. In
agreement with observations for TR agonist 4 and its ana-
logues,21 the substituents on the inner ring (R1) exerted a
significant effect on the binding potency with the order being I
> Br > Cl > Me. To explore the effects of the side chain in
this series, we prepared compounds 40 (Y ) CH2CH2), 57a (Y
) OCH2), and 61b (Y ) NHCH2). Contrary to the observations
made in the benzylphenyl series, these compounds had similar
binding potency. In addition, the analogue with a sulfur
connected side chain (67, Ki ) 42.1 nM) showed similar potency
when compared to the compound with an oxygen connected
side chain (57c, Ki ) 25.4 nM). Interestingly, the triiodo-
substituted analogue (48, R1 ) I, R2 ) I, Ki ) 26 nM) was the
only compound that showed better binding affinity toward TRR1
than TRꢀ1, though its activity was 30-fold weaker when
compared to compound 45 (R1 ) I, R2 ) i-Pr, Ki ) 0.84 nM).

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7081
Scheme 10. Synthesis of Prodrugs of Compound 22ca
a Reagents and conditions: (a) i-Pr2NEt, CH3CN, ICH2OC(O)R, room temp; (b) S-acetyl-2-thioethanol or 1-aryl-1,3-propane diol, pyridine, DMF,
dicyclohexylcarbodiimide, 70 °C; (c) (i) (COCl)2, CH2Cl2, DMF, 50 °C; (ii) i-Pr2NEt, H2N-C(RR′)-COOEt, CH2Cl2, 0 °C.
Table 1. Binding Affinities for Human TR
Table 2. Cholesterol Lowering Activity of Selected Compounds
compd
% change of TPC,a mean ( SEM
vehicle
22b
22c
22e
32
40
45
57a
57b
61b
-5.0 ( 2.2
-7.5 ( 6.1
-37.2 ( 2.3
-20.1 ( 12.4
-32.3 ( 5.6
-34.5 ( 2.7
-39.4 ( 3.1
-42.6 ( 6.7
-44.7 ( 8.2
-47.7 ( 5.0
compd
R1
R2
X
Y
TRR1 Kia TRꢀ1 Kia
1b
2
3
4
13
16
22a
22b
22c
22d
22e
22f
27
29
32
38a
38b
38c
40
0.33
0.51
1.09
7.79
0.68
0.47
0.32
0.24
I
I
O
O
CH2CH(NH2)
NHCO
1416
285
897
61.6
35.2
1165
30.5
3296
594
378
28.4
1760
303
235
271
36.0
89.7
9.72
2.95
106
6.64
146
87.0
31.3
9.10
128
a Cholesterol-fed rats were treated by intraperitoneal injection with 0.2
mg/kg of the indicated compounds. The percentage change in total plasma
cholesterol from pretreatment levels was calculated on a pairwise basis based
on the total plasma cholesterol levels measured 24 h after treatment. Data
represent mean values ( SEM, n ) 6.
Me
Me
Me
Me
Me
Me
i-Pr
Me
Et
i-Pr
Ph
CH2 OCH2
CH2 OCH2
CH2 OCH2
CH2 OCH2
s-Bu CH2 OCH2
OMe i-Pr
CH2 OCH2
trend for TR agonist 3 and its ether analogue, compound 22c
(X ) CH2, Y ) OCH2, Ki ) 2.95 nM) demonstrated greater
binding activity when compared to 57c (X ) O, Y ) OCH2, Ki
) 25.4 nM).
Me
Me
Me
Me
Cl
Br
Br
I
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
I
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
CH2 OCH2CH2
CH2 CH2CH2
CH2 NHCH2
O
O
O
O
O
O
O
O
O
O
O
O
CH2
CH2
CH2
52.3
15.5
Effects on Total Plasma Cholesterol. Nine phosphonic acids
with potent binding affinities (Ki < 10 nM) were evaluated in
the cholesterol-fed rat model for their potential TR agonist
effects. Each compound was administered by intraperitoneal
injection at 0.2 mg/kg, and total plasma cholesterol (TPC) was
measured after 24 h. The results are summarized in Table 2.
Compound 22c, the most potent compound from the benzylphe-
nyl series, showed a 37% reduction of TPC. Surprisingly,
compound 22b did not have any cholesterol lowering effect,
suggesting the rapid metabolism of this compound or a lack of
agonist activity. All five diphenyl ether analogues lowered TPC
more than 30%, with 61b showing almost 48% reduction of
TPC.
CH2CH2
CH2
42.1
1.84
16.0
18.6
3.74
183
186
10.3
143
2.50
0.84
26.0
2.51
0.97
25.4
30.5
1.51
42.1
45
48
I
CH2
57a
57b
57c
61a
61b
67
Br
I
Me
Cl
Br
Me
OCH2
OCH2
OCH2
NHCH2
NHCH2
SCH2
a Ki values are calculated means from duplicate measurements of IC50
using the Cheng-Prushoff equation and expressed as nM.
The role of the bridging moiety between the phenyl rings and
side chain in influencing binding affinity has been well studied
for the carboxylic acid TR ligands.53 Consistent with the SAR
Effects on Heart and Liver mGPDH. In an effort to
understand whether these phosphonic acids indeed have tissue-

7082 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
Figure 1. Effects of 7-day treatment with selected TR-agonists on liver or heart mGPDH activity. Normal rats were infused with the indicated
TR-agonists at a dose of 1 (mg/kg)/day. Data represent mean values ( SEM, n ) 6.
selective TR agonist effects, compounds 22c and 48 and their
Table 3. Cholesterol Lowering Activity at 0.5 mg/kg (po), ED50, and
corresponding carboxylic acid analogues 3 and 3,5-diiodo-4-
(4′-hydroxy-3′-iodophenoxy)phenylacetic acid (TRIAC) were
tested by chronic infusion into normal Sprague-Dawley rats.
TR agonist activity in the liver and heart was assessed by
measuring the activity of mitochondrial glycerol-3-phosphate
dehydrogenase (mGPDH), an enzyme known to be induced by
T3.54,55 The use of mGPDH activity permitted the comparison
of TR agonist activity of all compounds using the same end
point in both organs. Compounds were administered by osmotic
pump infusion at a dose of 1 (mg/kg)/day for 7 days. The dose
of T3 chosen for the experiment had been used to produce
cardiac changes consistent with overt hyperthyroidism in
euthyroid rats.56 Results are shown in Figure 1. Both the
carboxylic acid and the phosphonic acid analogues induced liver
mGPDH to the levels not significantly different from those
observed in the T3-treated animals. On the other hand, no
significant increase in heart mGPDH activity was observed for
the phosphonic acid analogues, while the carboxylic acid
analogues induced cardiac mGPDH activity to the levels
observed with T3.
Prodrug Evaluation. Prodrugs 68-83 were evaluated for
their ability to lower cholesterol orally (po) in vivo in the
cholesterol-fed rat assay over 24 h at a dose of 0.5 mg/kg (Table
3). All esterase-sensitive prodrugs (68-70) decreased cholesterol
levels in the 20-33% range with the bis-POM prodrug 68
showing the largest decrease. Cyclic 1-(aryl)-1,3-propanyl
prodrugs 72-78 reduced cholesterol to varying degrees based
on the nature of the activating group. While the 3-fluorophenyl
prodrug 75 had the largest decrease of all the cyclic 1-(aryl)-
1,3-propanyl prodrugs, the 3-bromophenyl prodrug 74 did not
achieve any reduction in cholesterol. The 3-chlorophenyl (72)
and 3-pyridyl (78) prodrugs had similar efficacy. Likewise, the
diamide prodrugs 79-83 showed a large variation in cholesterol
lowering as a function of the amino acid. The glycine (79) and
alanine diamide prodrugs (80) had comparable activity, but as
the size of the R-substitution of the amino acid increased, a
significant decrease in activity was observed, with the phenyl-
alanine diamide prodrug 83 exhibiting no cholesterol reduction.
A representative prodrug from each series was selected for
ED50 determination in the cholesterol-fed rat assay. Dose
responses for prodrugs 68, 72, and 79 are presented in Figure
2 with their respective ED50 values and maximal pharmacologi-
cal responses reported in Table 3. Compounds 68 and 72 had
similar ED50 values (0.4-0.5 mg/kg) and maximal responses,
while prodrug 79 appeared slightly more efficacious with an
ED50 of 0.1 mg/kg and a comparable maximal cholesterol
reduction.
Maximal Cholesterol Decrease in the 24 h Cholesterol-Fed Rat Assay
cholesterol
cholesterol
lowering
lowering ED50,
mg/kg po (max
cholesterol decrease)
compd
(% decrease)a
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
33
24
24
20
36
28
0
46
29
29
39
42
42
23
13
0
0.7 (46%)
0.48 (55%)
0.1 (48%)
a Cholesterol-fed rats were treated by oral gavage with 0.5 mg/kg of the
indicated compounds. The percentage change in total plasma cholesterol
from pretreatment levels was calculated on a pairwise basis based on the
total plasma cholesterol levels measured 24 h after treatment. Data represent
mean values ( SEM, n ) 6.
Figure 2. Oral dose-response curves for cholesterol lowering for
compounds 68, 72, and 79 in the 24 h cholesterol-fed rat assay.
Esterase sensitive prodrugs 68 and 79 were evaluated in
human liver S9 for their activation rates and amounts of prodrug
remaining after an incubation period of 1 h at 100 µM (Table
4). Prodrug 68 had a cleavage rate twice that of prodrug 79

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7083
Table 4. Rate of Activation and Product Distribution of Esterase
Sensitive Prodrugs 68 and 79 in Human Liver S9 after 1 h of Incubation
at 100 µM
some differences between the analogues based on TR agonist
3 (benzylphenyl series) and those based on TR agonist 4
(diphenyl ether series). While the methyl group is well tolerated
at the 3,5-positions in the benzylphenyl series, halogens are the
preferred groups at the same positions in the diphenyl ether
series. Moreover, the bridging group between the side chain
and the phenyl ring has a significant impact on the binding
affinity in the benzylphenyl series, as evidenced by the fact that
compound 29 (Y ) CH2CH2, 31.3 nM) was less potent when
compared to 22c (Y ) OCH2, 2.95 nM), while in the diphenyl
ether series compound 40 (Y ) CH2CH2, 2.50 nM) had the
same binding potency as compound 57a (Y ) OCH2, 2.51 nM).
The data suggest that the side chains in the two analogue series
may have different interactions with the receptor in the vicinity
of the phosphonic acid moiety, or the longer carbon-carbon
bonds of the methylene bridge between the two phenyl rings
(1.54 versus 1.39 Å for C-O) in the benzylphenyl series may
have an important effect on the binding of the side chain with
TR. Overall, the binding data indicate that compounds with an
isopropyl group at the 3′-position, halogen at the 3,5-positions,
and a side chain with one or two atoms between the phosphonic
acid and the phenyl ring are expected to show optimal potency.
Although most phosphonic acid ligands display reduced TR
binding affinity when compared with their corresponding
carboxylic acids, these compounds offer the opportunity for
further studies about the nature of receptor interactions and in
vivo activity.
% identified metabolite distribution
compd rate ((pmol/min)/mg)a compd 22c
monoacid
prodrug
68
79
134
73
11
24
79
6
11
70
a Rate of production of the parent phosphonic acid 22c.
based on the rate of appearance of parent phosphonic acid 22c.
However, even after 1 h of incubation there was still some
prodrug remaining for the very rapidly cleaved bis-POM prodrug
68 (11% remaining) and a much larger amount for the
bisamidate prodrug 79 (70% remaining). Since minimization
of extrahepatic exposure to prodrug was highly desired, prodrug
72 was selected as the lead compound for further characteriza-
tion (vide infra).
Pharmacokinetics for Prodrug 72. Pharmacokinetic param-
eters for prodrug 72 were evaluated in the rat at 3 mg/kg (Table
5). Following oral administration of prodrug 72 the Cmax and
t1/2 values of compound 72 were 0.012 ( 0.008 µg/mL and
0.95 ( 0.35 h, respectively, while the Cmax and t1/2 values of
the parent phosphonic acid 22c generated were 0.018 ( 0.003
µg/mL and 9.25 ( 6.24 h, respectively. After oral administration
of prodrug 72, the plasma AUClast values for the parent
compound 22c were greater (up to ∼8-fold) than those for the
prodrug 72, suggesting first pass clearance of 72 by the liver.
The oral bioavailability of prodrug 72, calculated on the basis
of plasma AUC of compound 72 following oral vs intravenous
administration, was estimated at ∼10%. A similar calculation
based on plasma levels of phosphonic acid 22c following oral
vs intravenous administration of 72 indicates a relative oral
bioavailability of 39%. The lower value for prodrug 72 is an
indication of high first-pass clearance.
Traditionally, TR ligands are evaluated in a cellular reporter
assay to establish functional activity. However, these assays use
transfected cultured cell lines that, unlike primary hepatocytes,
are unable to effectively transport highly negatively charged
phosphonic acids. As such, we evaluated functional activity
using an in vivo assay for cholesterol lowering. In addition, to
further increase our throughput, we developed a 24 h cholesterol-
fed rat assay as a screening tool to evaluate agonism in vivo.
While for many species it takes several days of dosing to achieve
stable drug-lowered cholesterol levels, in the case of the
cholesterol-fed rat, it has been our experience that similar
cholesterol reductions are observed following 24 h, 4 days, or
7 days of daily treatment. The screening dose of 0.2 mg/kg was
chosen on the basis of the reported ED50 for cholesterol lowering
in the 7-day model for TR agonists 4 (30 (µg/kg)/day,
subcutaneous)21 and 3 (62 (µg/kg)/day, oral),20 and we have
obtained similar ED50 values for 4 and 3 in this assay. While
this screening protocol may not have given as much information
as a full dose response, it was rapid and sufficient for quickly
identifying lead compounds for subsequent evaluation of the
lipid lowering dose response relative to various extrahepatic
effects.28 The studies from the 24 h cholesterol-fed rat model
further established that phosphonic acid ligands are potent TR
agonists in the liver.
Discussion
TRs represent an attractive target for lipid control but only
if the well-known dose-limiting side effects of TR agonists
can be avoided. Recent efforts have focused on eliminating
cardiac side effects through development of TRꢀ1-selective
TR agonists. Compounds 3 and 4 exhibit a 10-fold selectivity
for TRꢀ1 and a rightward shift in the dose-response curve
for various cardiac indices relative to the dose response for
cholesterol lowering. These compounds, however, result in
decreased weight and a suppression of the hypothalamic-pi-
tuitary-thyroid (HPT) axis at lipid lowering doses, suggest-
ing that both are capable of extrahepatic activity. In human
clinical trials, the TRꢀ1-selective TR agonist 5 is reported
to result in significant lipid lowering without affecting the
heart. Decreases in both T4 and T3 were also noted and
possibly due to activation of TRꢀ1 in the pituitary.
On the basis of its cholesterol lowering efficacy, 22c was
chosen for the evaluation of liver-selective TR activity. The
mGPDH results demonstrate not only that 22c and 48 are full
agonists in the liver but also that they, unlike their corresponding
carboxylic acid analogues, can induce significant TR activity
in the liver without showing detectable effects in cardiac tissue.
While mGPDH activity may not be directly related to cardio-
vascular safety, this experiment was designed to test our initial
hypothesis that phosphonic acids are much more selective
toward hepatic tissues than nonhepatic tissues. The fact that
compound 22c is a full agonist in the liver but does not increase
the mGPDH activity in the heart supports our initial hypothesis
and suggests that PA TR agonists may result in a greater cardiac
Our efforts focused on the discovery of PA-based TR agonists
with the hope that this approach would selectively activate TRs
in the liver while avoiding activation of TRs in extrahepatic
tissues. Because of their high negative charge at physiological
pH, phosphonic acids usually enter the liver by active transport
and are generally associated with very low volumes of distribution.
The binding data demonstrate that phosphonic acids can be
excellent ligands for human TRꢀ1. Consistent with the observa-
tions for carboxylic acid ligands, the substituents on the biaryl
system and the length of the side chain have a major impact on
the binding affinity. The similar SAR profile for the phosphonic
acid series suggests that these compounds may bind to the TR
in a similar pattern as the carboxylic acids. However, there are

7084 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Table 5. Pharmacokinetic Parameters for Compound 72 in Rats
Boyer et al.
compd 72, 3 mg/kg iva
compd 72, 3 mg/kg pob
parameter
AUClast
units
compd 72 mean ( SD
compd 22c mean ( SD
compd 72 mean ( SD
compd 22c mean ( SD
mg·h/L
µg/mL
0.26 ( 0.04
0.60 ( 0.22
0.0 ( 0.0
1.23 ( 0.15
1.20 ( 0.20
11.55 ( 1.93
14.82 ( 3.99
0.34 ( 0.06
0.092 ( 0.017
0.60 ( 0.15
8.82 ( 2.38
4.49 ( 0.28
0.026 ( 0.011
0.012 ( 0.008
2.1 ( 1.0
0.95 ( 0.35
2.49 ( 0.72
0.135 ( 0.035
0.018 ( 0.003
3.6 ( 1.1
9.25 ( 6.24
7.91 ( 1.60
c
Cmax
c
Tmax
h
h
h
half-life
MRTd
Cl
(L/h)/kg
L/kg
h
Vss
MATe
F
1.29 ( 0.72
9.9 ( 4.0
3.4 ( 1.74
39.2 ( 11.2
%
a The prodrug was dosed in propylene glycol. b The prodrug was dosed in PEG-400. c Back-extrapolation to Y-axis. d Mean residence time. e Mean
absorption time.
TI. These results were further confirmed during the advanced
characterization of prodrug 72 where TI values of >125 and
>7.5 for cholesterol lowering relative to cardiovascular side
effects and TSH suppression, respectively, were observed.28
However, as is usually the case with phosphonic acid-based
drugs, 22c has low oral bioavailability and required a prodrug
approach to further its development.28 Fortunately, numerous
phosphonate prodrug strategies have been developed to circum-
vent these limitations, with a few applications leading to clinical
drugs (adefovir dipivoxil, tenofovir disoproxil, pradefovir).
Therefore, a series of prodrugs, representing the major classes
of prodrugs developed to enhance the oral bioavailability of
phosphonic acids, was synthesized in one step from phosphonic
acid 22c.
over the remaining fraction of esterase-sensitive prodrugs
entering the systemic circulation after oral administration, and
not being fully activated to prevent their entry into extrahepatic
tissues, favored the selection of prodrug 72 as the lead
compound. In addition to being stable in extrahepatic tissues, a
cyclic 1-(aryl)-1,3-propanyl prodrug has the advantage of
selectively generating the parent drug in the liver, further
minimizing extrahepatic exposure.27
Upon further evaluation of its pharmacokinetic parameters
in rats, prodrug 72 was found to have good oral bioavailability
and hepatic uptake (rat F ) 40%) and was therefore selected
as the lead compound for evaluation as a new oral therapy for
the treatment of hypercholesterolemia.
Determination of TR binding affinities for early lead prodrug
series established that prodrugs of phosphonic acids are weak
ligands (data not shown), as evidenced by the binding affinities
for prodrug 72 (TRꢀ1 Ki ) 14.6 µM and TRR1 Ki ) 12.5 µM).28
All prodrugs were evaluated orally for efficacy in the 24 h
cholesterol-fed rat assay. All esterase-sensitive prodrugs were
efficacious in this model with the bis-POM prodrug 68 being
significantly better than the others. As previously observed with
other parent drugs,49,57 no correlation was observed between
the electronic properties of the activating aryl group of cyclic
1-(aryl)-1,3-propanyl prodrugs and the in vivo results. However,
for the diamide prodrugs, there was a good correlation between
the in vivo efficacy and the size of the R-substituent on the
amino acid. As the size of the substituent increased from methyl
to benzyl, the in vivo efficacy decreased (H, Me > (Me)2 >
i-Pr > Bn). Prodrugs 68, 72, and 79 were selected as
representative prodrugs of each class for ED50 determination.
Prodrug 72 was among the most efficacious of the cyclic
1-(aryl)-1,3-propanyl prodrugs tested and was selected on the
basis of our experience with the cyclic 1-(3-chlorophenyl)-1,3-
propanyl prodrug of the antiviral drug adefovir (pradefovir) and
the results generated during its development, including a 48-
week phase 2 trial in patients with chronic hepatitis B.58 All
three prodrugs had ED50 values below 1 mg/kg, with the diamide
prodrug 79 having the lowest.
Prodrugs 68 and 79 require activation by esterases for
generation of the parent TR agonist 22c. Because of the wide
distribution of these enzymes in tissues, the fraction of the
prodrug not absorbed by the liver after oral administration has
the potential to enter extrahepatic tissues if it is not quickly
and fully cleaved in the plasma. In contrast, cyclic 1-(aryl)-
1,3-propanyl prodrugs are stable in plasma and extrahepatic
tissues because of their unique and specific activation mecha-
nism in the liver.27 Evaluation of esterase-sensitive prodrugs
68 and 79 in esterase-rich human liver S9 still showed the
presence of intact prodrug after 1 h of incubation at 100 µM
despite good rates of activation for both prodrugs. Concerns
Conclusions
A series of phosphonic acid TR agonists has been discovered.
The carboxylic acid group of the known TR ligands can be
replaced with a phosphonic acid moiety while retaining potent
TR binding affinity as well as cholesterol lowering efficacy in
the cholesterol-fed rat model. More importantly, the potent full
TR agonist 22c demonstrated selective TR activation in the liver
vs heart. On the basis of its binding affinity, cholesterol lowering
efficacy, and liver-selective TR agonism, 22c was chosen for
synthesis of a series of prodrugs to circumvent its low oral
bioavailability. Potent cholesterol lowering activity, selective
liver activation, and good oral bioavailability led to the selection
of prodrug 72 for further characterization as a potential drug
candidate for the treatment of hypercholesterolemia.
Experimental Section
General Information. All reactions were carried out under a
nitrogen atmosphere. NMR spectra were recorded on Varian
Gemini-200, Varian Mercury-300, and Varian Mercury-500 spec-
trometers. Coupling constants (J) and chemical shifts (δ) are
expressed in Hz and ppm, respectively. Mass spectra were recorded
on a Perkin-Elmer API 2000 spectrometer. All solvents and reagents
were purchased from commercial sources and used without further
purification. Thin layer chromatography was performed on EM
Science silica gel 60 F254 plates. Silica gel 60 (230-400 mesh)
from EM Science was used when compounds were purified by
column chromatography. Melting points were recorded on a
Thomas-Hoover capillary melting point apparatus and were not
corrected. Elemental analyses were performed by Robertson Mi-
crolit Laboratories, Inc., Madison, NJ, and NuMega Resonance
Laboratories, Inc., San Diego, CA. All protocols involving animal
experimentation were reviewed and approved by the Metabasis
Therapeutics IACUC (Institution Animal Care and Use Committee)
following the guidelines established by the NRC “Guide for the
Care and Use of Laboratory Animals”.
General Method A. Synthesis of Benzylphenyl Analogues
22a-f. Key intermediates 20a-f were prepared according to the
known method from a variety of MOM-protected phenols 18a-e

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7085
and TIPS-protected aldehydes 17a,b.39 Alkylation of phenols 20a-f
with diethyl tosyloxymethylphosphonate (or diethyl trifluorometh-
ylsulfonyloxymethylphosphonate) in the presence of Cs2CO3 at
room temperature gave phosphonates 21a-f, which were typically
purified by column chromatography on silica gel. Final compounds
22a-f were obtained by deprotection with TMSBr.
[3,5-Dimethyl-4-(4′-hydroxy-3′-methylbenzyl)phenoxy]meth-
ylphosphonic Acid (22a). 1H NMR (300 MHz, DMSO-d6): δ 8.99
(s, 1 H), 6.68-6.525 (m, 5 H), 6.71 (s, 2 H), 4.03 (d, J ) 7.5 Hz,
2 H), 3.77 (s, 2 H), 2.15 (s, 6 H), 2.02 (s, 3 H). LC-MS m/z )
335 [C17H21O5P - H]. Anal. (C17H21O5P·0.6H2O) C, H.
[3,5-Dimethyl-4-(3′-ethyl-4′-hydroxybenzyl)phenoxy]meth-
ylphosphonic Acid (22b). 1H NMR (300 MHz, DMSO-d6): δ 8.96
(s, 1 H), 6.72-6.49 (m, 5 H), 4.03 (d, J ) 10.2 Hz, 2 H), 3.78 (s,
2 H), 2.48 (q, J ) 8.1 Hz, 2 H), 2.16 (s, 6 H), 1.06 (t, J ) 7.5 Hz,
[3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy]meth-
ylphosphonic Acid (22c). To a stirring solution of 18c (4.50 g, 17.3
mmol) in THF (60 mL) at -78 °C was slowly added a solution of
n-BuLi (6.90 mL, 17.2 mmol). The reaction mixture was stirred at
-78 °C for 50 min, and to it was added a solution of 17a (4.40 g,
14.4 mmol) in THF (5 mL). The reaction mixture was stirred at
-78 °C for 1 h, quenched with saturated aqueous NH4Cl, and
diluted with Et2O (20 mL). The mixture was allowed to warm to
room temperature, and the organic layer was separated. The organic
solution was dried over MgSO4, filtered, and concentrated under
reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-ethyl acetate
(9:1) to afford 19c as a colorless oil (6.40 g, 92%). 1H NMR (300
MHz, CDCl3): δ 7.18 (s, 1 H), 6.94 (m, 2 H), 6.57 (s, 2 H), 6.21
(d, J ) 3.2 Hz, 1 H), 5.20 (s, 2 H), 3.48 (s, 3 H), 3.35 (m, 1 H),
2.20 (s, 6 H), 1.10-1.40 (m, 45 H). Rf ) 0.42 (hexanes-ethyl
acetate, 9:1).
3
H). LC-MS m/z
) 349 [C18H23O5P - H]. Anal.
(C17H21O5P·1.3H2O·0.3CH2Cl2) C, H.
[3,5-Dimethyl-4-(4′-hydroxy-3′-phenylbenzyl)phenoxy]meth-
ylphosphonic Acid (22d). 1H NMR (300 MHz, DMSO-d6): δ 9.29
(s, 1 H), 6.60-7.60 (m, 8 H), 4.02 (d, J ) 15 Hz, 2 H), 2.18 (s, 2
H). LC-MS m/z
(C29H41O11P·1.7H2O·0.4CH3OH) C, H.
[3,5-Dimethyl-4-(3′-sec-butyl-4′-hydroxybenzyl)phenoxy]meth-
ylphosphonic Acid (22e).
)
399 [C29H41O11P
+
H]+. Anal.
1H NMR (200 MHz, DMSO-d6): δ 8.92
(s, 1 H), 6.77 (s, 1 H), 6.68 (s, 2 H), 6.61 (d, J ) 8.6 Hz, 1 H),
6.47 (d, J ) 8.6 Hz, 1 H), 4.02 (d, J ) 10.2 Hz, 2 H), 3.78 (s, 2
H), 2.90 (m, 1 H), 1.45 (q, J ) 6.6 Hz, 2 H), 1.05 (d, J ) 7.0 Hz,
3 H), 0.74 (t, J ) 7.0 Hz, 3 H). LC-MS m/z ) 379 [C
20H27O5P +
H]+
. Anal. (C20H27O5P·0.7H2O) C, H.
A mixture of 19c (6.40 g, 13.2 mmol) and Pd-C (0.55 g, 10%)
in acetic acid-ethyl acetate (44 mL, 1:9) was stirred under a H2
atmosphere for 16 h and filtered through a Celite plug. The solvent
was removed under reduced pressure, and the residue was dissolved
in THF (40 mL). The organic solution was cooled to 0 °C, and to
it was added a solution of TBAF (20.0 mL, 20.0 mmol). After 5
min, the reaction mixture was stirred at room temperature for 20
min, quenched with water, and extracted with Et2O (20 mL). The
organic layer was dried over MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-ethyl acetate
(1:5) to afford 20c as a colorless oil (3.50 g, 85%). 1H NMR (300
MHz, CD3OD): δ 6.90 (m, 2 H), 6.65 (dd, J ) 11.2, 3.0 Hz, 1 H),
6.49 (s, 2 H), 5.13 (s, 2 H), 3.88 (s, 2 H), 3.44 (s, 3 H), 3.25 (m,
1 H), 2.13 (s, 6 H), 1.13 (d, J ) 6.8 Hz, 6 H); Rf ) 0.52
(hexanes-ethyl acetate, 5:1).
To a stirring mixture of NaH (0.85 g, 21.4 mmol) in DMF (40
mL) at 0 °C was added a solution of 20c (5.60 g, 17.8 mmol) in
DMF (7 mL). The reaction mixture was stirred at room temperature
for 1 h and cooled to 0 °C. To it was added a solution of diethyl
tosyloxymethylphosphonate (6.89 g, 21.4 mmol) in DMF (7 mL).
The reaction mixture was stirred at room temperature for 16 h,
quenched with MeOH (4 mL) and H2O (100 mL), and extracted
with Et2O (100 mL × 2). The combined organic layers were dried
over MgSO4, filtered, and concentrated under reduced pressure. The
crude product was purified by column chromatography on silica
gel, eluting with hexanes-acetone (3:1) to afford 21c as a colorless
oil (5.32 g, 64%). 1H NMR (300 MHz, DMSO-d6): δ 6.94 (d, J )
3.0 Hz, 1 H), 6.87 (d, J ) 9.0 Hz, 1 H), 6.73 (s, 2 H), 6.58 (m, 1
H), 5.14 (s, 2 H), 4.36 (d, J ) 9.0 Hz, 2 H), 4.10 (m, 4 H), 3.85
(s, 2 H), 3.36 (s, 3 H), 3.21 (m, 1 H), 2.17 (d, J ) 6.0 Hz, 6 H),
1.25 (m, 6 H), 1.12-1.10 (d, J ) 6.0 Hz, 6 H). Rf ) 0.62
(hexanes-acetone, 1:1).
[3,5-Dimethoxy-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy]meth-
ylphosphonic Acid (22f). 1H NMR (300 MHz, DMSO-d6): δ 8.86
(s, 1 H), 6.96 (d, J ) 1.8 Hz, 1 H), 6.64 (dd, J ) 1.8 Hz, 8.4 Hz,
1 H), 6.54 (d, J ) 8.4 Hz, 1 H), 6.27 (s, 2 H), 4.07 (d, J ) 10.2
Hz, 2 H), 3.74 (s, 6 H), 3.64 (s, 2 H), 3.08 (m, 1 H), 1.08 (d, J )
6.9 Hz, 6 H). LC-MS m/z ) 397 [C19H25O7P + H]+. Anal.
(C19H25O7P·0.4CH3CO2C2H5 ·0.9H2O) C, H.
[3,5-Dimethoxy-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy]eth-
ylphosphonic Acid (27). To a stirring solution of 20c (1.00 g, 3.18
mmol) in DMF (30 mL) was added Cs2CO3 (5.18 g, 15.9 mmol)
followed by 1,2-dibromoethane (1.64 g, 19.1 mmol). The reaction
mixture was stirred at 60 °C for 48 h, cooled to room temperature,
and diluted with ethyl acetate (10 mL). The mixture was washed
with H2O and brine, dried over MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-ethyl acetate
1
(4:1) to afford 25 as an oil (0.26 g, 16%). H NMR (300 MHz,
CDCl3): δ 6.94 (m, 2 H), 6.67 (m, 3 H), 5.18 (s, 2 H), 4.32 (m, 2
H), 3.95 (s, 2 H), 3.68 (m, 2 H), 3.51 (s, 3 H), 3.37 (s, 3 H), 3.32
(m, 1 H), 2.26 (s, 6 H), 1.22 (d, J ) 6.0 Hz, 6 H). Rf ) 0.91
(hexanes-ethyl acetate, 4:1).
A mixture of 25 (0.15 g, 0.36 mmol) and triethyl phosphite (0.18
g, 1.07 mmol) in DMF (2 mL) was heated under reflux for 4 h.
The reaction mixture was cooled to room temperature, diluted with
ethyl acetate, and washed with H2O. The organic layer was dried
over MgSO4, filtered, and concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel,
eluting with hexanes-acetone (1:1) to afford 26 as an oil (0.085
1
g, 50%). H NMR (300 MHz, DMSO-d6): δ 6.96 (m, 1 H), 6.89
(m, 1 H), 6.62 (m, 3 H), 5.16 (s, 2 H), 4.12 (m, 2 H), 4.07 (m, 4
H) 3.86 (s, 2 H), 3.37 (s, 3 H), 3.22 (m, 1 H), 2.30 (m, 2 H), 2.17
(s, 6 H), 1.25 (m, 6 H), 1.12 (d, J ) 6.0 Hz, 6 H). Rf ) 0.10
(hexanes-acetone, 1:1).
Deprotection of 26 with TMSBr as described above afforded 27
as a brown solid (0.05 g, 87%): mp 58-61 °C. LC-MS m/z )
379 [C20H27O5P + H]+. 1H NMR (300 MHz, CD3OD): δ 6.84 (s,
1 H), 6.66 (s, 2 H), 6.56 (m, 2 H), 4.26 (m, 2 H), 3.90 (s, 2 H),
3.22 (m, 1 H), 2.30 (m, 1 H), 2.22 (s, 6 H), 1.15 (d, J ) 6.0 Hz,
6 H). Anal. (C20H27O5P·0.6H2O) C, H.
To a solution of 21c (0.90 g, 1.94 mmol) in CH2Cl2 (10 mL) at
0 °C was added TMSBr (3.80 mL, 28.8 mmol). The reaction
mixture was allowed to warm to room temperature and stirred for
16 h. The solvent was removed under reduced pressure, and the
residue was treated with CH3CN-H2O (1:1, 10 mL). The solvent
was removed under reduced pressure, and the residue was treated
with toluene (10 mL). The mixture was sonicated for 10 min,
filtered, and washed with hexanes to afford 22c as a pink solid
2-[3,5-Dimethoxy-4-(4′-hydroxy-3′-isopropylbenzyl)phenyl]eth-
ylphosphonic Acid (29). To a solution of 20c (0.60 g, 1.73 mmol)
and DMAP (0.85 g, 6.92 mmol) in CH2Cl2 (20 mL) at 0 °C was
slowly added Tf2O (0.44 mL, 2.60 mmol). The reaction mixture
was stirred at 0 °C for 2 h and quenched by H2O (10 mL). The
organic layer was dried over Na2SO4, filtered, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-ethyl acetate
1
(0.64 g, 91%). H NMR (300 MHz, CD3OD): δ 6.80 (d, J ) 1.5
Hz, 1 H), 6.73 (s, 2 H), 6.55 (m, 2 H), 4.18 (d, J ) 10.5 Hz, 2 H),
3.87 (s, 2 H), 3.21 (m, 1 H), 2.19 (s, 6 H), 1.12 (d, J ) 7.5 Hz, 6
H). 13C NMR (125 MHz, CD3OD): δ 20.5, 23.0, 28.0, 34.4, 63.4,
64.7, 114.8, 115.8, 126.3, 126.5, 131.9, 132.0, 135.8, 139.4, 153.4,
158.4, 158.5. LC-MS m/z ) 365 [C19H25O5P + H]+. Anal.
(C19H25O5P·0.9H2O) C, H.
1
(9:1) to afford 23 as a light-yellow oil (0.83 g, 100%). H NMR

7086 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
(300 MHz, DMSO-d6): δ 7.09 (s, 1 H), 6.87 (s, 2 H), 6.80 (s, 2
H), 5.15 (s, 2 H), 3.84 (s, 6 H), 3.81 (s, 2 H), 3.36 (s, 3 H), 3.20
(m, 1 H), 1.14 (d, J ) 6.6 Hz, 6 H). Rf ) 0.73 (hexanes-ethyl
acetate, 9:1).
mixture was stirred at -78 °C for 20 min, and diethyl trifluorom-
ethylsulfonyloxymethylphosphonate (0.16 g, 0.76 mmol) was added.
The reaction mixture was stirred at -78 °C for 1 h, allowed to
warm to room temperature, and stirred for 4 h. The reaction was
quenched with aqueous NH4Cl and extracted with ethyl acetate (10
mL). The organic solution was dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude product was purified
by column chromatography on silica gel, eluting with hexanes-ethyl
A mixture of 23 (0.50 g, 1.73 mmol), Et3N (0.60 mL, 4.32
mmol), Pd(PPh3)2Cl2 (0.08 g, 0.10 mmol), and diethyl vinylphos-
phonate (0.25 mL, 1.60 mmol) in DMF (3 mL) was heated at 80
°C for 24 h. The reaction mixture was cooled to room temperature,
diluted with ethyl acetate (10 mL), and washed with aqueous
NaHCO3. The organic solution was dried over Na2SO4, filtered,
and concentrated under reduced pressure. The crude product was
purified by column chromatography on silica gel, eluting with
hexanes-acetone (1:1) to afford 28 as a yellow oil (0.23 g, 45%).
1H NMR (300 MHz, CDCl3): δ 7.50 (d, J ) 17.4 Hz, 1 H), 7.29
(s, 1 H), 7.11 (m, 2 H), 6.72 (s, 2 H), 6.22 (t, J ) 17.1 Hz, 1 H),
5.17 (s, 2 H), 4.21 (m, 4 H), 3.96 (s, 2 H), 3.87 (s, 6 H), 3.49 (s,
3 H), 3.31 (m, 1 H), 1.40 (t, J ) 6.9 Hz, 6 H), 1.23 (d, J ) 6.6 Hz,
6 H). Rf ) 0.40 (hexanes-acetone, 1:1).
A mixture of 28 (0.10 g, 0.2 mmol) and Pd-C (0.02 g, 10%) in
MeOH (20 mL) was stirred under a H2 atmosphere at room
temperature for 16 h and filtered through a Celite plug. The solvent
was removed under reduced pressure, and the residue was dissolved
in CH2Cl2 (5 mL). Deprotection with TMSBr as described above
afforded 29 as a pink foam in 91% yield. 1H NMR (200 MHz,
DMSO-d6): δ 8.88 (s, 1 H), 7.01 (d, J ) 1.8 Hz, 1 H), 6.71 (dd, J
) 1.8 Hz, J ) 8.0 Hz, 1 H), 6.55 (d, J ) 8.4 Hz, 1 H), 6.5 (s, 2
H), 3.76 (s, 6 H), 3.69 (s, 2 H), 3.08 (m, 1 H), 2.72 (m, 2 H), 1.82
(m, 2 H), 1.08 (d, J ) 7.0 Hz, 6 H). LC-MS m/z ) 395 [C20H27O6P
+ H]+. Anal. (C20H27O6P·1.3H2O) C, H.
1
acetate (1:1) to afford 31 as an oil (0.21 g, 49%). H NMR (300
MHz, DMSO-d6): δ 7.00 (s, 2 H), 6.94 (m, 1 H), 6.90 (m, 1 H),
6.64 (m, 1 H), 5.16 (s, 2 H), 4.09 (d, J ) 6.0 Hz, 2 H), 4.00 (m,
4 H), 3.8 (m, 2 H), 3.37 (s, 3 H), 3.22 (m, 1 H), 2.20 (s, 6 H), 1.40
(s, 9 H), 1.27 (m, 6 H), 1.13 (m, 6 H). Rf ) 0.20 (hexanes-ethyl
acetate, 2:3).
To a stirring solution of 31 (0.19 g, 0.34 mmol) in MeOH (4
mL) at 0 °C was added 2 N HCl (1.68 mL, 3.37 mmol). The
reaction mixture was stirred at room temperature for 48 h, cooled
to 0 °C, neutralized with NaHCO3, and extracted with ethyl acetate
(20 mL). The organic solution was dried over MgSO4, filtered, and
concentrated under reduced pressure. The residue was purified by
column chromatography on silica gel, eluting with hexanes-ethyl
acetate (2:3) to afford the desired phosphonate as a white solid
1
(0.07 g, 51%). H NMR (300 MHz, DMSO-d6): δ 8.95 (s, 1 H),
6.84 (m, 1 H), 6.63 (m, 1 H), 6.50 (m, 1 H), 6.45 (s, 2 H), 5.39 (m,
1H), 4.06 (s, 6 H), 3.74 (s, 2 H), 3.51 (m, 2 H), 3.13 (m, 1 H),
2.09 (s, 6 H), 1.20 (m, 6 H), 1.11 (d, J ) 6.0 Hz, 6 H). Rf ) 0.29
(hexanes-ethyl acetate, 4:1).
Deprotection of 31 with TMSBr as described above afforded 32
1
as an off-white powder in 79% yield: mp 147-150 °C. H NMR
(300 MHz, DMSO-d6): δ 8.97 (s, 1 H), 6.86 (m, 1 H), 6.59 (m, 1
H), 6.49 (m, 1 H), 6.45 (s, 2 H), 3.74 (s, 2 H), 3.20 (d, J ) 12.0
Hz, 2 H), 3.13 (m, 1 H), 2.10 (s, 6 H), 1.12 (d, J ) 6.0 Hz, 6 H).
[4-(4′-Hydroxy-3′-isopropylbenzyl)-3,5-dimethylphenylamino]m-
ethylphosphonic Acid (32). A solution of 23 (2.04 g, 4.57 mmol),
Et3N (1.27 mL, 9.14 mmol), 1,3-bis(diphenylphosphino)propane
(0.19 mL, 0.45 mmol), MeOH (3.71 mL, 91.4 mmol), and Pd(OAc)2
(0.10 g, 0.46 mmol) in DMF (25 mL) was heated at 90 °C under
a CO atmosphere (60 psi) in a Parr bomb for 16 h. The reaction
mixture was cooled to 0 °C, diluted with ethyl acetate (25 mL),
and washed with H2O. The organic solution was dried over Na2SO4,
filtered, and concentrated under reduced pressure. The crude product
was purified by column chromatography on silica gel, eluting with
hexanes-ethyl acetate (4:1) to afford 24 as an oil (1.52 g, 93%).
1H NMR (300 MHz, DMSO-d6): δ 7.68 (s, 2 H), 6.97 (m, 1 H),
6.91 (m, 2 H), 6.20 (m, 1 H), 5.16 (s, 2 H), 4.01 (s, 3 H), 3.85 (s,
3 H), 3.21 (m, 1 H), 2.28 (s, 6 H), 1.14 (d, J ) 6.0 Hz, 6 H). TLC
conditions: Rf ) 0.42 (hexanes-ethyl acetate, 4:1).
LC-MS m/z
)
364 [C19H26NO4P
-
H]+. Anal.
(C19H26NO4P·1.0H2O·0.2HBr·0.2CH3CO2CH2CH3) C, H, N, Br.
General Method B. Synthesis of Diphenyl Ether Analogues
38a-c. Key intermediates 35a-c were prepared from the iodonium
salt 33 and commercially available methyl benzoates 34a-c
according to the known method.16 Reduction of 35a-c with
DIBAL-H followed by treatment of the resulting benzyl alcohols
with CBr4 and PPh3 gave benzyl bromides 36a-c, which underwent
Michaelis-Arbuzov reaction with triethyl phosphite to provide
phosphonates 37a-c. Final compounds 38a-c were obtained by
deprotection with TMSBr and BBr3.
[3,5-Dichloro-4-(4′-hydroxy-3′-isopropylphenoxy)]benzylphos-
phonic Acid (38b). To a mixture of 33 (4.55 g, 8.88 mmol) and
copper powder (0.88 g, 13.8 mmol) in CH2Cl2 (40 mL) at 0 °C
was added a solution of Et3N (1.06 mL, 3.71 mmol) and 34b (1.65
g, 6.90 mmol) in CH2Cl2 (20 mL). The reaction mixture was stirred
at room temperature for 72 h and filtered through a Celite plug.
The solvent was removed under reduced pressure and the residue
was purified by column chromatography on silica gel, eluting with
To a stirring solution of 24 (0.75 g, 2.11 mmol) in MeOH (20
mL) at 0 °C was added 1 N NaOH (12.6 mL, 12.6 mmol). The
reaction mixture was heated at 50 °C for 16 h, cooled to 0 °C, and
acidified with 2 N HCl. The mixture was extracted with ethyl acetate
(20 mL) and washed with H2O. The organic solution was dried
over Na2SO4, filtered, and concentrated under reduced pressure to
1
afford the desired acid as a white solid (0.71 g, 98%). H NMR
1
(300 MHz, DMSO-d6): δ 12.76 (s, 1 H), 7.65 (s, 2 H), 6.98 (m, 1
H), 6.91 (m, 1 H), 6.60 (m, 1 H), 5.17 (s, 2 H), 4.00 (s, 2 H), 3.37
(s, 3 H), 3.23 (m, 1 H), 2.27 (s, 6 H), 1.14 (d, J ) 6.0 Hz, 6 H).
To a solution of the above acid (0.70 g, 2.04 mmol), tert-butanol
(0.75 g, 10.22 mmol), and Et3N (0.71 g, 5.11 mmol) in toluene
(30 mL) was added diphenylphosphoryl azide (0.44 mL, 2.04
mmol). The reaction mixture was heated under reflux for 16 h,
cooled to room temperature, and poured into a cold solution of
0.25 N HCl (30 mL). The mixture was extracted with ethyl acetate
(20 mL) and washed with H2O. The organic solution was dried
over MgSO4, filtered, and concentrated under reduced pressure. The
crude product was purified by column chromatography on silica
gel, eluting with hexanes-ethyl acetate (9:1) to afford 30 as a
yellow oil (0.63 g, 75%). 1H NMR (300 MHz, DMSO-d6): δ 9.16
(s, 1 H), 7.16 (s, 2 H), 6.96 (m, 1 H), 6.90 (m, 1 H), 6.62 (m, 1 H),
5.16 (s, 2 H), 3.86 (s, 2 H), 3.37 (s, 3 H), 3.22 (m, 1 H), 2.15 (s,
6 H), 1.48 (m, 9 H), 1.23 (d, J ) 6.0 Hz, 6 H). Rf ) 0.72
(hexanes-ethyl acetate, 7:3).
hexanes-acetone (6:1) to afford 35b as a solid (2.02 g, 80%). H
NMR (300 MHz, DMSO-d6): δ 8.10 (m, 1 H), 6.85 (m, 2 H), 6.50
(m, 1 H), 3.90 (s, 3 H), 3.76 (s, 3 H), 3.21 (m, 1 H), 1.14 (d, J )
6.0 Hz, 6 H). Rf ) 0.51 (hexanes-acetone, 6:1).
To a mixture of 35b (1.40 g, 3.37 mmol) in THF (10 mL) at 0
°C was added a solution of DIBAL-H (8.12 mL, 8.12 mmol). The
reaction mixture was stirred at room temperature for 16 h, quenched
with cold 1 N HCl, and extracted with ethyl acetate (15 mL). The
organic layer was washed with H2O, dried over MgSO4, filtered,
and concentrated under reduced pressure to afford the benzyl alcohol
as an off-white solid (0.94 g, 100%). 1H NMR (300 MHz, DMSO-
d6): δ 7.54 (s, 2 H), 6.81 (m, 2 H), 6.40 (m, 1 H), 5.51 (m, 1 H),
4.54 (d, J ) 6.0 Hz, 2 H), 3.75 (s, 3 H), 3.21 (m, 1 H), 1.13 (d, J
) 6.0 Hz, 6 H). Rf ) 0.27 (hexanes-acetone, 6:1).
To a stirred solution of PPh3 (0.42 g, 1.61 mmol) and CBr4 (0.534
g, 1.61 mmol) in Et2O (15 mL) at room temperature was added
the above benzyl alcohol (0.50 g, 1.46 mmol). The reaction mixture
was stirred at room temperature for 16 h, filtered, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-acetone (9:1)
To a mixture of 30 (0.315 g, 0.76 mmol) in THF (8 mL) at -78
°C was added a solution of LDA (0.46 g, 0. 91 mmol). The reaction

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7087
to afford 36b as a solid (0.32 g, 54%). 1H NMR (300 MHz, DMSO-
d6): δ 7.77 (s, 2 H), 6.82 (m, 2 H), 6.38 (m, 1 H), 4.75 (s, 2 H),
3.75 (s, 3 H), 3.22 (m, 1 H), 1.13 (d, J ) 6.0 Hz, 6 H). Rf ) 0.46
(hexanes-acetone, 4:1).
and concentrated under reduced pressure. The crude product was
purified by column chromatography on silica gel, eluting with
hexanes-acetone (3:2) to afford the phosphonate as a colorless oil.
The desired product was dissolved in MeOH (12 mL), and to it
was added Pd-C (10%, 0.33 g). The mixture was stirred under a
H2 atmosphere for 16 h, filtered through a Celite plug, and
concentrated under reduced pressure to afford 42 as an oil (0.9 g,
84%). 1H NMR (300 MHz, CD3OD): δ 7.12 (d, J ) 8.4 Hz, 2 H),
6.73 (d, J ) 8.4 Hz, 2 H), 4.05 (m, 4 H), 3.16 (s, 1 H), 3.09 (s, 1
H), 1.26 (t, J ) 6.9 Hz, 6 H). LC-MS m/z ) 245 [C11H17O4P +
H]+. Rf ) 0.50 (hexanes-acetone, 1:1).
A mixture of 36b (0.61 g, 1.51 mmol) and triethyl phosphite
(0.61 g, 3.56 mmol) in DMF (2 mL) was heated under reflux for
4 h. The reaction mixture was cooled to room temperature, diluted
with ethyl acetate, and washed with H2O. The organic layer was
concentrated under reduced pressure and the residue was purified
bycolumnchromatographyonsilicagel,elutingwithhexanes-acetone
1
(7:3) to afford 37b as an oil (0.59 g, 85%). H NMR (300 MHz,
DMSO-d6): δ 7.55 (s, 2 H), 6.88 (d, J ) 9.0 Hz, 1 H), 6.75 (d, J
) 3.0 Hz, 1 H), 6.43 (m, 1 H), 4.01 (m, 4 H), 3.75 (s, 3 H), 3.41
(m, 2 H), 3.22 (m, 1 H), 1.20 (m, 6 H), 1.12 (d, J ) 6.0 Hz, 6 H).
Rf ) 0.22 (hexanes-acetone, 4:1).
To a solution of 42 (0.50 g, 2.05 mmol) in CH2Cl2 (12 mL) at
room temperature was added bis(pyridine)iodonium tetrafluorobo-
rate (1.67 g, 4.50 mmol). The reaction mixture was stirred at room
temperature for 1 h, and the solvent was removed under reduced
pressure. The crude product was purified by column chromatog-
raphy on silica gel, eluting with hexanes-acetone (1:1) to afford
To a solution of 37b (0.59 g, 1.28 mmol) in CH2Cl2 (10 mL) at
-30 °C was added TMSBr (2.53 mL, 19.2 mmol). The reaction
mixture was stirred at room temperature for 16 h, and the solvent
was removed under reduced pressure. The residue was dissolved
in CH2Cl2 (25 mL) and cooled to -78 °C. To it was added a
solution of BBr3 (19.0 mL, 19.0 mmol). The reaction mixture was
stirred at -78 °C for 10 min, allowed to warm to room temperature,
and stirred for 16 h. The mixture was poured into ice and extracted
with ethyl acetate (10 mL). The organic layer was washed with
H2O, dried over MgSO4, and filtered. The solvent was removed
under reduced pressure to afford 38b as a brown solid (0.20 g,
40%): mp 178-181 °C. LC-MS m/z ) 391 [C16H17Cl2O5P - H]-.
1H NMR (300 MHz, DMSO-d6): δ 9.08 (s, 1 H), 7.48 (s, 2 H),
6.72 (m, 2 H), 6.25 (m, 1 H), 3.18 (m, 1 H), 3.00 (d, J ) 21.0 Hz,
2 H), 3.11 (m, 1 H), 1.14 (d, J ) 6.0 Hz, 6 H). Anal. (C16H17Cl2-
O5P·0.2CH3CO2CH2CH3 ·0.5H2O) C, H.
[3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylphenoxy)]benzylphos-
phonic Acid (38a). Mp 79-82 °C. LC-MS m/z ) 351 [C18H23O5P
+ H]+. 1H NMR (300 MHz, CD3OD): δ 6.93 (s, 2 H), 6.51 (m, 2
H), 6.13 (m, 1 H), 3.13 (m, 1 H), 2.98 (d, J ) 21.0 Hz, 2 H), 1.96
(s, 6 H), 1.04 (d, J ) 6.0 Hz, 6 H). Anal. (C18H23O5P·1.2H2O) C,
H.
[3,5-Dibromo-4-(4′-hydroxy-3′-isopropylphenoxy)]benzylphos-
phonic Acid (38c). Mp 145 °C. LC-MS m/z ) 536 [C20H25Br2O5P
+ H]+. 1H NMR (300 MHz, CD3OD): δ 7.53 (s, 2 H), 6.50 (m, 2
H), 6.23 (m, 1 H), 3.98 (m, 4 H), 3.11 (m, 1 H), 1.21 (m, 6 H),
1.02 (d, J ) 6.0 Hz, 6 H). Anal. (C20H25Br2O5P) C, H.
2-[3,5-Dibromo-4-(4′-hydroxy-3′-isopropylphenoxy)phenyl]eth-
ylphosphonic Acid (40). To a solution of dimethyl methylphos-
phonate (0.06 g, 0.48 mmol) in THF (3 mL) at -78 °C was slowly
added a solution of LDA (0.25 mL, 0.50 mmol). After 30 min, a
solution of 36c (0.20 g, 0.40 mmol) in THF was added. The reaction
mixture was stirred at -78 °C for 5 min, allowed to warm to room
temperature, and stirred for 2 h. The reaction mixture was quenched
with aqueous NH4Cl (10 mL) and extracted with Et2O (10 mL).
The organic layer was dried over MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-acetone (1:1)
to afford 39 (0.09 g, 43%) as a colorless oil: 1H NMR (300 MHz,
CD3OD): δ 7.64 (s, 2 H), 6.82 (d, J ) 10.0 Hz, 1 H), 6.75 (d, J )
4.2 Hz, 1H), 6.44 (dd, J ) 2.8, 10.2 Hz, 1 H), 3.79 (d, J ) 2.8 Hz,
6 H), 3.76 (s, 3 H), 3.30 (m, 1 H), 2.94 (m, 2 H), 2.23 (m, 2 H),
1.17 (d, J ) 7.0 Hz, 6 H). LC-MS m/z ) 537 [C20H25 Br2O5P +
H]+. Rf ) 0.50 (hexanes-acetone, 1:1).
Deprotection of 39 with TMSBr and BBr3 as described above
gave 40 as an off-white solid: mp 56-59 °C. 1H NMR (200 MHz,
DMSO-d6): δ 9.02 (s, 1 H), 7.65 (s, 2 H), 6.64 (m, 2 H), 6.21 (dd,
J ) 2.8, 10.2 Hz, 1 H), 3.14 (m, 1 H), 2.79 (m, 2 H), 1.87 (m, 2
H), 1.11 (d, J ) 7.0 Hz, 6 H). LC-MS m/z ) 495 [C17H19 Br2O5P
+ H]+. Anal. (C17H19 Br2O5P·0.5H2O) C, H.
3,5-Diiodo-4-(4′-hydroxy-3′-isopropylphenoxy)benzylphospho-
nic Acid (45). A mixture of 41 (1.0 g, 4.40 mmol) and triethyl
phosphite (1.0 mL, 5.80 mmol) in DMF (2.8 mL) was heated at
155 °C for 4 h. The reaction mixture was cooled to room
temperature, quenched with H2O (10 mL), and extracted with ethyl
acetate (20 mL). The organic layer was dried over MgSO4, filtered,
1
43 as a white solid (0.92 g, 90%). H NMR (300 MHz, CD3OD):
δ 7.67 (d, J ) 2.7 Hz, 2 H), 4.05 (m, 4 H), 3.10 (d, J ) 12.9 Hz,
2 H), 1.28 (t, J ) 6.9 Hz, 6 H). LC-MS m/z ) 497 [C11H16I2O4P
+ H]+. Rf ) 0.57 (hexanes-acetone, 1:1).
Coupling of 43 with 33 as described above gave 44 as a colorless
oil in 85% yield. 1H NMR (300 MHz, CD3OD): δ 7.87 (d, J ) 2.7
Hz, 2 H), 6.80 (d, J ) 6.7 Hz, 2 H), 6.65 (s, 1 H), 6.40 (dd, J )
2.7 Hz, 6.9 Hz, 2 H), 4.09 (m, 4 H), 3.78 (s, 3 H), 3.24 (d, J )
12.9 Hz, 2 H), 3.20 (m, 1 H), 1.28 (t, J ) 6.9 Hz, 6 H), 1.13 (d,
J ) 6.8 Hz, 6 H). LC-MS m/z ) 497 [C11H16I2O4P + H]+. Rf )
0.90 (hexanes-acetone, 1:1).
Deprotection of 44 with TMSBr and BBr3 as described above
1
afforded 45 as a white solid in 92% yield. H NMR (300 MHz,
CD3OD): δ 7.85 (d, J ) 2.4 Hz, 2 H), 6.59 (m, 2 H), 6.28 (dd, J
) 2.4, 8.7 Hz, 1 H), 3.22 (m, 1 H), 3.18 (s, 1 H), 3.08 (s, 1 H),
1.18 (d, J ) 6.9 Hz, 6 H). LC-MS m/z ) 575 [C
16H17I2O4P +
H]+
. Anal. (C16H17I2O5P·0.3 H2O·0.5CH3OH) C, H, I.
3,5-Diiodo-4-(4′-hydroxy-3′-iodophenoxy)benzylphosphonic Acid
(48). To a mixture of 43 (0.40 g, 0.81 mmol), 4-(tert-butyldimeth-
ylsiloxy)phenylboronic acid (0.61 g, 2.42 mmol), Cu(OAc)2 (0.18
g, 0.99 mmol), and 4 Å molecular sieves (1.20 g) in CH2Cl2 (7
mL) was added a solution of pyridine (0.4 mL, 4.8 mmol) and Et3N
(0.7 mL, 4.8 mmol). The reaction mixture was stirred at room
temperature for 48 h, filtered through a Celite plug, and concentrated
under reduced pressure. The residue was purified by column
chromatography on silica gel, eluting with hexanes-acetone (3:1)
to afford the desired product as a white solid. The resulting product
was dissolved in THF (3 mL) and cooled to 0 °C. To it was added
a solution of TBAF (0.30 mL, 0.30 mmol), and the reaction mixture
was stirred at room temperature for 20 min. The solvent was
removed under reduced pressure and the crude product was purified
bycolumnchromatographyonsilicagel,elutingwithhexanes-acetone
1
(1:1) to afford 46 as a white solid (0.06 g, 13%). H NMR (300
MHz, CD3OD): δ 7.84 (s, 2 H), 6.70 (d, J ) 8.4 Hz, 2 H), 6.56 (d,
J ) 8.4 Hz, 2 H), 4.15 (m, 4 H), 3.25 (d, J ) 12.8 Hz, 2 H), 1.30
(m, 6 H). LC-MS m/z ) 589 [C17H19I2O5P + H]+. Rf ) 0.40
(hexanes-acetone, 1:1).
To a solution of 46 (0.10 g, 0.17mmol) in EtOH (4 mL) at 0 °C
was added 40% aqueous MeNH2 (0.40 mL) followed by a solution
of KI (0.16 g, 0.51 mmol) and I2 (0.06 g, 0.23 mmol) in H2O (0.5
mL). The reaction mixture was stirred at 0 °C for 1 h, quenched
with H2O, and extracted with ethyl acetate (10 mL). The organic
layer was dried over MgSO4, filtered, and concentrated under
reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with MeOH-CH2Cl2 (1:19)
to afford 47 as a yellow solid (0.10 g, 69%). 1H NMR (300 MHz,
CD3OD): δ 7.85 (s, 2 H), 7.00 (d, J ) 5.2 Hz, 1 H), 6.74 (d, J )
8.4 Hz, 1 H), 6.64 (dd, J ) 3.2, 8.4 Hz, 1 H), 4.18 (m, 5 H), 3.08
(m, 1 H), 2.78 (m, 1 H), 1.36 (m, 6 H). LC-MS m/z ) 715
[C17H18I3O5P + H]+. Rf ) 0.55 (MeOH-CH2Cl2, 1:19).
Deprotection of 47 with TMSBr as described above gave 48 as
1
a white solid in 90%. H NMR (300 MHz, CD3OD): δ 7.86 (d, J
) 2.4 Hz, 2 H), 6.99 (d, J ) 6.4 Hz, 1 H), 6.74 (d, J ) 8.7 Hz, 1
H), 6.62 (dd, J ) 2.4, 8.7 Hz, 1 H), 3.15 (s, 1 H), 3.08 (s, 1 H).

7088 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
LC-MSm/z)659[C13H10I3O5P+H]+.Anal.(C13H10I3O5P·1.6H2O·
0.5CH3OH) C, H, I.
2 H), 6.63 (d, J ) 9.0 Hz, 1 H), 6.57 (d, J ) 3.0 Hz, 1 H), 6.18
(m, 1 H), 4.10 (d, J ) 9.0 Hz, 2 H), 1.10 (d, J ) 6.0 Hz, 6 H).
LC-MS m/z ) 589 [C16H17I2O6P - H]- Anal. (C16H17I2O6P ·
0.4H2O) C, H.
[3,5-Dibromo-4-(4′-hydroxy-3′-isopropylphenoxy)phenoxy]meth-
ylphosphonic Acid (57a). Mp 77-80 °C. LC-MS m/z ) 495
[C16H17Br2O6P - H]-. 1H NMR (300 MHz, DMSO-d6): δ 8.99 (s,
1 H), 7.42 (s, 2 H), 6.63 (m, 2 H), 6.22 (m, 1 H), 4.21 (d, J ) 9.0
Hz, 2 H), 3.11 (m, 1 H), 1.10 (d, J ) 6.0 Hz, 6 H). Anal.
(C16H17Br2O6P·0.2C6H14) C, H.
General Method C. Synthesis of Compounds with an Oxygen-
Linked Side Chain 57a-c. Compounds 57a-c were prepared by
selective alkylation of the key intermediates 55a-c with diethyl
trifluoromethylsulfonyloxymethylphosphonate followed by depro-
tection with TMSBr. Phenols 55a-c were synthesized from
compounds 49 and 51 with different methods.
[3,5-Diiodo-4-(4′-hydroxy-3′-isopropylphenoxy)phenoxy]meth-
ylphosphonic Acid (57b). To a solution of 51 (0.2 g, 0.93 mmol)
in CH2Cl2 (9.3 mL) at 0 °C was added bis(pyridine)iodonium
tetrafluoroborate (0.76 g, 2.06 mmol). The reaction mixture was
stirred at room temperature for 1 h, and the solvent was removed
under reduced pressure. The residue was purified by column
chromatography on silica gel, eluting with hexanes-acetone (9:1)
[3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylphenoxy)phenoxy]me-
thylphosphonic Acid (57c). Mp 60-64 °C. LC-MS m/z ) 367
1
[C18H23O6P + H]+. H NMR (200 MHz, DMSO-d6): δ 8.88 (s, 1
H), 6.76 (s, 2 H), 6.60 (m, 2 H), 6.17 (m, 1 H), 4.04 (d, J ) 15.0
Hz, 2 H), 3.13 (m, 1 H), 2.01 (s, 6 H), 1.10 (d, J ) 6.0 Hz, 6 H).
Anal. (C18H23O6P·0.7H2O) C, H.
1
to afford 52b as an off-white solid (0.22 g, 50%). H NMR (300
MHz, DMSO-d6): δ 9.60 (s, 1 H), 8.06 (m, 2 H), 7.72 (s, 2 H),
7.59 (m, 3 H). Rf ) 0.45 (hexanes-acetone, 4:1).
3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylphenoxy)phenol (55c).
To a mixture of 33 (4.80 g, 9.38 mmol) and Cu powder (0.79 g,
12.5 mmol) in CH2Cl2 (15 mL) at 0 °C was added a solution of 49
(0.94 g, 6.26 mmol) and Et3N (0.96 mL, 6.89 mmol) in CH2Cl2
(15 mL). The reaction mixture was stirred at room temperature for
72 h and filtered through a Celite plug. The solvent was removed
under reduced pressure and the residue was purified by column
chromatography on silica gel, eluting with hexanes-acetone (19:
1) to afford 50 as an oil (2.00 g, 100%). 1H NMR (300 MHz,
DMSO-d6): δ 9.96 (s, 1 H), 7.75 (s, 2 H), 6.85 (m, 1 H), 6.73 (m,
1 H), 6.36 (m, 1 H), 3.74 (s, 3 H), 3.19 (m, 1 H), 2.15 (s, 6 H),
1.12 (d, J ) 6.0 Hz, 6 H). Rf ) 0.51 (hexanes-acetone, 17:3).
To a solution of 50 (0.18 g, 0.60 mmol) in CH2Cl2 (6 mL) at 0
°C was added m-chloroperoxybenzoic acid (0.22 g, 0.905 mmol).
The reaction mixture was stirred at room temperature for 16 h.
The solvent was removed under reduced pressure, and the residue
was dissolved in ethyl acetate (10 mL). The organic solution was
washed with saturated NaHCO3 (10 mL) and concentrated under
reduced pressure. To the residue was added MeOH (5 mL) and 1
N NaOH (1.81 mL, 1.81 mmol). The reaction mixture was stirred
at room temperature for 4 h, acidified with 2 N HCl, extracted with
ethyl acetate (10 mL), and washed with H2O. The organic solution
was dried over MgSO4, filtered, and concentrated under reduced
pressure. The residue was purified by preparatory TLC with
hexanes-acetone (4:1) as mobile phase to afford 54c as an oil (0.08
To a mixture of 33 (0.77 g, 1.51 mmol) and Cu powder (0.13 g,
2.01 mmol) in CH2Cl2 (4.4 mL) at 0 °C was added a solution of
52b (0.47 g, 1.00 mmol) and Et3N (0.15 mL, 1.10 mmol) in CH2Cl2
(4 mL). The reaction mixture was stirred at room temperature for
24 h and filtered through a Celite plug. The solvent was removed
under reduced pressure and the residue was purified by column
chromatography on silica gel, eluting with hexanes-acetone (9:1)
1
to afford 53b as an off-white solid (0.61 g, 98%). H NMR (300
MHz, DMSO-d6): δ 8.10 (m, 2 H), 7.96 (s, 2 H), 7.73 (m, 1 H),
7.60 (m, 2 H), 6.85 (d, J ) 9.0 Hz, 1 H), 6.73 (d, J ) 3.0 Hz, 1
H), 6.35 (m, 1 H), 3.74 (s, 3 H), 3.21 (m, 1 H), 1.13 (d, J ) 6.0
Hz, 6 H). Rf ) 0.42 (hexanes-acetone, 9:1).
A mixture of 53b (0.10 g, 0.16 mmol) and 1 N NaOH (0.81
mL, 0.81 mmol) in MeOH (1.63 mL) was stirred at room
temperature for 24 h. The reaction mixture was neutralized with 2
N HCl, diluted with H2O, and extracted with CH2Cl2 (10 mL ×
2). The combined organic layers were concentrated under reduced
pressure and the crude product was purified by preparatory TLC
with hexanes-acetone (4:1) as mobile phase to afford 54b as an
1
off-white solid (0.08 g, 95%). H NMR (300 MHz, DMSO-d6): δ
9.99 (s, 1 H), 7.28 (s, 2 H), 6.81 (d, J ) 12.0 Hz, 1 H), 6.67 (d, J
) 3.0 Hz, 1 H), 6.30 (m, 1 H), 3.72 (s, 3 H), 3.18 (m, 1 H), 1.11
(d, J ) 6.9 Hz, 6 H). Rf ) 0.42 (hexanes-acetone, 7:3).
1
g, 47%). H NMR (200 MHz, DMSO-d6): δ 9.17 (s, 1 H), 6.82
To a stirred solution of 54b (0.28 g, 0.55 mmol) in CH2Cl2 (17
mL) at -78 °C was added BBr3 (13.1 mL, 13.1 mmol, 1 M solution
in CH2Cl2). The reaction mixture was stirred at -78 °C for 10 min,
allowed to warm to room temperature, and stirred for 16 h. The
reaction mixture was poured into ice and extracted with CH2Cl2
(20 mL × 2). The combined organic layers were dried over MgSO4,
filtered, and concentrated under reduced pressure. The crude product
was purified by column chromatography on silica gel, eluting with
hexanes-acetone (7:3) to afford 55b as an off-white solid (0.18 g,
66%). 1H NMR (300 MHz, DMSO-d6): δ 9.95 (s, 1 H), 8.91 (s, 1
H), 7.27 (s, 2 H), 6.62 (d, J ) 9.0 Hz, 1 H), 6.56 (d, J ) 3.0 Hz,
1 H), 6.18 (m, 1 H), 3.72 (s, 3 H), 3.14 (m, 1 H), 1.10 (d, J ) 6.0
Hz, 6 H). Rf ) 0.28 (hexanes-acetone, 7:3).
To a mixture of 55b (0.07 g, 0.14 mmol) and Cs2CO3 (0.22 g,
0.67 mmol) in DMF (1.35 mL) at 0 °C was added diethyl
trifluoromethylsulfonyloxymethylphosphonate (0.04 g, 0.14 mmol).
The reaction mixture was stirred at room temperature for 5 h,
quenched with 1 N HCl, and extracted with ethyl acetate (10 mL
× 2). The combined organic layers were dried over MgSO4, filtered,
and concentrated under reduced pressure. The residue was purified
by preparatory TLC with hexanes-acetone (3:2) as mobile phase
to afford 56b as an off-white solid (0.048 g, 55%). 1H NMR (300
MHz, DMSO-d6): δ 8.95 (s, 1 H), 7.57 (s, 2 H), 6.63 (d, J ) 9.0
Hz, 1 H), 6.56 (d, J ) 3.0 Hz, 1 H), 6.19 (m, 1 H), 4.51 (d, J )
9.0 Hz, 2 H), 4.08 (m, 4 H), 3.14 (m, 1 H), 1.25 (m, 6 H), 1.10 (d,
J ) 6.0 Hz, 6 H). Rf ) 0.29 (hexanes-acetone, 3:2).
(m, 1 H), 6.70 (m, 1 H), 6.51 (s, 2 H), 6.32 (m, 1 H), 3.71 (s, 3 H),
3.18 (m, 1 H), 1.95 (s, 6 H), 1.12 (d, J ) 6.0 Hz, 6 H). Rf ) 0.44
(hexanes-acetone, 4:1).
General Method D. Synthesis of Compounds with a Nitrogen-
Linked Side Chain 61a,b. The final compounds were prepared from
commercially available anilines 58a,b by Boc protection followed
by coupling with the iodonium salt 33, N-alkylation and deprotec-
tion with TMSBr and BBr3.
[3,5-Dichloro-4-(4′-hydroxy-3′-isopropylphenoxy)phenylami-
no]methylphosphonic Acid (61a). To a solution of 58a (4.0 g, 22.5
mmol) in THF (25 mL) was added di-tert-butyl dicarbonate (5.88
g, 27.0 mmol). The reaction mixture was heated under reflux for
2.5 h, and the solvent was removed under reduced pressure. The
crude product was purified by column chromatography on silica
gel, eluting with hexanes-acetone (9:1) to afford the desired Boc-
protected aniline as an off-white solid (5.80 g, 93%). 1H NMR
(300 MHz, DMSO-d6): δ 9.70 (s, 1 H), 9.44 (s, 1 H), 7.46 (s, 2
H), 1.48 (s, 9 H). Rf ) 0.39 (hexanes-acetone, 7:3).
To a mixture of 33 (2.76 g, 5.39 mmol) and Cu powder (0.46 g,
7.18 mmol) in CH2Cl2 (20 mL) at 0 °C was added a solution of
Et3N (0.55 mL, 3.95 mmol) and the above phenol (1.00 g, 3.59
mmol) in CH2Cl2 (10 mL). The reaction mixture was stirred at room
temperature for 14 h and filtered through a Celite plug. The solvent
was removed under reduced pressure and the residue was purified
bycolumnchromatographyonsilicagel,elutingwithhexanes-acetone
1
Deprotection of 56b with TMSBr as described above afforded
57b as an off-white solid in 63% yield: mp 180 °C, dec. LC-MS
m/z ) 589 [C16H17I2O6P - H]-. LC-MS m/z ) 589 [C16H17I2O6P
(7:3) to afford 59a as an off-white solid (1.45 g, 95%). H NMR
(300 MHz, DMSO-d6): δ 9.81 (s, 1 H), 7.68 (m, 2 H), 6.79 (m, 2
H), 6.42 (m, 1 H), 3.75 (s, 3 H), 3.20 (m, 1 H), 1.51 (s, 9 H), 1.33
(d, J ) 6.0 Hz, 6 H). Rf ) 0.64 (hexanes-acetone, 7:3).
1
- H]-. H NMR (300 MHz, DMSO-d6): δ 8.95 (s, 1 H), 7.51 (s,

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7089
To a mixture of 59a (0.40 g, 0.94 mmol) in THF (12 mL) at 0
°C was added NaH (0.06 g, 1.22 mmol, 60% dispersion in oil).
The reaction mixture was stirred at room temperature for 1 h and
cooled to 0 °C. To the stirring mixture was added diethyl
trifluoromethylsulfonyloxymethylphosphonate (0.18 g, 0.94 mmol).
The reaction mixture was stirred at room temperature for 2 h,
quenched with H2O, and extracted with ethyl acetate (10 mL). The
organic layer was dried over MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-ethyl acetate
(10 mL) at 0 °C was added a solution of 65 (0.16 g, 0.53 mmol)
and Et3N (0.08 mL, 0.58 mmol) in CH2Cl2 (2 mL). The reaction
mixture was stirred at room temperature for 16 h and filtered
through a Celite plug. The solvent was removed under reduced
pressure and the crude product was purified by column chroma-
tography on silica gel, eluting with hexanes-ethyl acetate (2:1) to
afford 66 as a yellow oil (0.14 g, 60%). 1H NMR (200 MHz,
DMSO-d6): δ 7.24 (s, 2 H), 6.79 (d, J ) 8.8 Hz, 1 H), 6.72 (d, J
) 3.0 Hz, 1 H), 6.32 (dd, J ) 3.0, 8.8 Hz, 1 H), 4.02 (m, 4 H),
3.73 (s, 3 H), 3.45 (d, J ) 14.4 Hz, 2 H), 3.18 (m,1 H), 2.04 (s, 6
H), 1.15 (m, 12 H). Rf ) 0.51 (hexanes-ethyl acetate, 2:1).
[4-(4′-Hydroxy-3′-isopropylphenoxy)-3,5-dimethylphenylsulfa-
nylmethyl]phosphonic Acid (67). Deprotection of 66 with TMSBr
and BBr3 as described above gave 67 in 51% yield. 1H NMR (300
MHz, DMSO-d6): δ 8.91 (s, 1 H), 7.16 (s, 2 H), 6.64 (m, 2 H),
6.21 (dd, J ) 3.3, 8.7 Hz, 1 H), 4.13 (m, 3 H), 2.02 (s, 6 H), 1.11
(d, J ) 6.9 Hz, 6 H). LC-MS m/z ) 383 [C18H23O5PS + H]+.
Anal. (C18H23O5PS·0.15CF3COOH·0.2CH3CH2OCH2CH3) C, H.
Diethyl N-[3,5-Dimethyl-4-(3′-isopropyl-4′-methoxyphenoxy)]-
carbamonylphosphonate (15). A mixture of 1416 (0.1 g, 0.35 mmol)
and diphosgene (0.04 g, 0.19 mmol) in dioxane (3 mL) was heated
at 60 °C for 3 h. The reaction mixture was cooled to room
temperature, and the solvent was removed under reduced pressure.
To the residue was added a solution of diethyl phosphite (0.06 g,
0.42 mmol) in hexanes (1 mL) with 3 drops of Et3N. The reaction
mixture was heated under reflux for 3 h and cooled to room
temperature. The solvent was removed under reduced pressure and
the crude product was purified by column chromatography on silica
gel, eluting with hexanes-ethyl acetate (3:1) to afford 15 as an oil
(0.10 g, 64%). 1H NMR (300 MHz, CDCl3): δ 8.44 (s, 1 H), 7.17
(s, 2 H), 6.10-6.60 (m, 3 H), 4.10 (m, 4 H), 3.58 (s, 3 H), 3.07
(m, 1 H), 1.92 (s, 3 H), 1.93 (s, 3 H), 1.22 (m, 6 H), 0.99 (m, 6 H).
LC-MS m/z ) 450 [C23H32NO6P + H]+. Rf ) 0.30 (hexanes-ethyl
acetate, 3:1).
1
(3:2) to afford 60a as an oil (0.34 g, 63%). H NMR (300 MHz,
DMSO-d6): δ 7.64 (s, 2 H), 6.90 (m, 1 H), 6.76 (s, 1 H), 6.45 (m,
1 H), 4.95 (d, J ) 9.0 Hz, 2 H), 4.01 (m, 4 H), 3.76 (s, 3 H), 3.21
(m, 1 H), 1.43 (s, 9 H), 1.20 (m, 6 H), 1.13 (d, J ) 6.0 Hz, 6 H).
Rf ) 0.15 (hexanes-ethyl acetate, 3:2).
Deprotection of 60a with TMSBr and BBr3 as described above
afforded 61a as an off-white solid in 85% yield: mp 97-100 °C.
1
LC-MS m/z ) 405,407 [C16H18Cl2NO5P + H]+. H NMR (300
MHz, DMSO-d6): δ 9.02 (s, 2 H), 6.90 (m, 2 H), 6.71 (m, 2 H),
6.32 (m, 2 H), 3.36 (m, 2 H), 3.21 (m, 1 H), 1.17 (d, J ) 6.0 Hz,
6 H). Anal. (C16H18Cl2NO5P·0.1CH3CO2CH2CH3 ·0.3H2O) C, H,
N.
[3,5-Dibromo-4-(4′-hydroxy-3′-isopropylphenoxy)phenylami-
1
no]methylphosphonic Acid (61b). H NMR (200 MHz, DMSO-
d6): δ 8.95 (m, 1 H), 7.02 (s, 2 H), 6.63 (m, 2 H), 6.23 (m, 1 H),
3.31 (d, J ) 12.0 Hz, 2 H), 3.14 (m, 1 H), 1.12 (d, J ) 6.0 Hz, 6
H). LC-MS m/z
(C16H18Br2NO5P·0.7CH3COCH3 ·0.7H2O) C, H, N.
) 496 [C16H18Br2NO5P -
H]+. Anal.
2,6-Dimethyl-4-methylsulfanylphenoxytriisopropylsilane (63). To
a stirring solution of 62 (0.5 g, 1.4 mmol) in THF (15 mL) at -78
°C was added n-BuLi (2.5 M in hexanes, 0.56 mL). The reaction
mixture was stirred at -78 °C for 1 h, and to it was added
methyldisulfanylmethane (0.16 mL, 1.82 mmol). The reaction
mixture was allowed to warm to room temperature, stirred for 1 h,
quenched with saturated NH4Cl, and extracted with Et2O (8 mL).
The organic solution was dried over Na2SO4, filtered, and concen-
trated under reduced pressure to afford 63 as an oil (0.46 g, 100%).
1H NMR (300 MHz, DMSO-d6): δ 6.92 (s, 2 H), 2.41 (s, 3 H),
2.20 (s, 6 H), 1.29 (m, 3 H), 1.10 (d, J ) 7.2 Hz, 18 H). Rf ) 0.57
(hexanes-ethyl acetate, 49:1).
N-[3,5-Dimethyl-4-(3′-isopropyl-4′-methoxyphenoxy)]carbamo-
nylphosphonic Acid (16). Deprotection of 15 with TMSBr and BBr3
as described above afforded 16 as a yellow solid in 42% yield. 1H
NMR (300 MHz, CD3OD): δ 7.39 (s, 2 H), 6.60 (m, 2 H), 6.26
(m, 1 H), 3.23 (m, 1 H), 2.09 (s, 6 H), 1.14 (d, J ) 5.1 Hz, 6 H).
LC-MS m/z ) 380 [C18H22NO6P + H]+. Anal. (C18H22NO6P ·
0.2H2O·0.3CH3OH) C, H, N.
Diethyl
(3,5-Dimethyl-4-triisopropylsilanyloxyphenyl-
sulfanyl)methylphosphonate (64). To a stirring solution of 63 (2.18
g, 6.72 mmol) in CCl4 (25 mL) at room temperature was added
NCS (0.99 g, 7.39 mmol). The reaction mixture was stirred at room
temperature for 16 h and filtered through a Celite plug. The solvent
was removed under reduced pressure to afford crude product as a
colorless oil (2.4 g, 100%). The crude product was dissolved in
triethyl phosphite (1.5 mL) and heated at 180 °C for 30 min in a
microwave oven. The solvent was removed under reduced pressure
and the residue was purified by column chromatography on silica
gel, eluting with hexanes-ethyl acetate (1:1) to afford 64 as a
Diethyl 2-(4-Benzyloxyphenyl)-1-hydroxyiminoethylphospho-
nate (7). To a solution of 6 (4.0 g, 16.2 mmol) in THF (10 mL) at
room temperature was slowly added triethyl phosphite (3.33 mL,
19.5 mmol). The reaction mixture was stirred at room temperature
for 16 h, and the solvent was removed under reduced pressure.
The residue was treated with hexanes (20 mL) and filtered. The
solid was dissolved in pyridine (25 mL), and to it was added
hydroxylamine hydrochloride (1.96 g, 28 mmol). The reaction
mixture was stirred at room temperature for 72 h, and the solvent
was removed under reduced pressure. The crude product was
purified by column chromatography on silica gel, eluting with
hexanes-ethyl acetate (7:3) to afford 7 as a colorless oil (5.2 g,
1
yellow oil (1.6 g, 52%). H NMR (200 MHz, DMSO-d6): δ 7.09
(s, 2 H), 4.98 (m, 4 H), 3.31 (d, J ) 13.8 Hz, 2 H), 2.17 (s, 6 H),
1.25 (m, 9 H), 1.09 (d, J ) 7.0 Hz, 18 H). Rf ) 0.45 (hexanes-ethyl
acetate, 3:2).
1
85%). H NMR (300 MHz, CDCl3): δ 7.18-7.38 (m, 7 H), 6.80
(d, J ) 6.2 Hz, 2 H), 4.94 (s, 2 H), 3.80-4.10 (m, 4 H), 3.80 (s,
1 H), 3.76 (s, 1 H), 1.16 (t, J ) 6.0 Hz, 6 H). LC-MS m/z )
[C23H32NO6P + H]+. Rf ) 0.55 (hexanes-ethyl acetate, 3:2).
2-(4-Benzyloxyphenyl) 1-tert-Butoxycarbonylaminoethylphos-
phonate (8). To a mixture of 7 (2.0 g, 5.3 mmol) and NiCl2 (2.53
g, 10.6 mmol) in MeOH (40 mL) at room temperature was slowly
added NaBH4 (1.0 g, 26.4 mmol). The reaction mixture was stirred
at room temperature for 16 h, and the solvent was removed under
reduced pressure. The residue was treated with 10% aqueous KOH
(100 mL) and extracted with Et2O (2 × 100 mL). The combined
organic layers were dried over MgSO4, filtered, and concentrated
under reduced pressure. The residue was dissolved in THF (14 mL),
and to it was added (BOC)2O (0.74 g, 3.4 mmol). The reaction
mixture was heated under reflux for 4 h and cooled to room
temperature. The solvent was removed under reduced pressure and
the residue was purified by column chromatography on silica gel,
eluting with MeOH-CH2Cl2 (1:19) to afford 8 as colorless oil (1.12
Diethyl
(4-Hydroxy-3,5-dimethylphenylsulfanylmeth-
yl)phosphonate (65). To a stirring solution of 64 (1.6 g, 3.47 mmol)
in THF (20 mL) at room temperature was added a solution of TBAF
(5.2 mL, 1 M in THF). The reaction mixture was stirred at room
temperature for 2 h, and the solvent was removed under reduced
pressure. The residue was dissolved in ethyl acetate (20 mL) and
washed with H2O. The organic solution was dried over Na2SO4,
filtered, and concentrated under reduced pressure. The crude product
was purified by column chromatography on silica gel, eluting with
hexanes-ethyl acetate (5:1) to afford 65 as a yellow oil (0.90 g,
85%). 1H NMR (200 MHz, DMSO-d6): δ 8.41 (s, 1 H), 7.06 (s, 2
H), 3.98 (m, 4 H), 3.22 (d, J ) 13.6 Hz, 2 H), 2.12 (s, 6 H), 1.22
(d, J ) 7.2 Hz, 6 H). Rf ) 0.44 (hexanes-ethyl acetate, 4:1).
Diethyl [4-(4′-Methoxy-3′-isopropylphenoxy)-3,5-dimethyl-phe-
nylsulfanylmethyl]phosphonate (66). To a stirring mixture of 33
(0.35 g, 0.68 mmol) and Cu powder (0.05 g, 0.79 mmol) in CH2Cl2

7090 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
g, 46%). 1H NMR (300 MHz, CD3OD): δ 7.38 (m, 5 H), 7.13 (d,
J ) 8.4 Hz, 2 H), 6.88 (d, J ) 8.4 Hz, 2 H), 4.88 (s, 2 H), 4.12 (m,
5 H), 3.08 (m, 1 H), 2.70 (m, 1 H), 1.34 (m, 6 H). LC-MS m/z )
464 [C24H34NO6P + H]+. Rf ) 0.45 (MeOH-CH2Cl2, 1:19).
Diethyl 1-tert-Butoxycarbonylamino-2-(3,5-diiodo-4-hydrox-
yphenyl)ethylphosphonate (9). A mixture of 8 (1.1 g, 2.4 mmol)
and Pd-C (0.23 g, 10%) in MeOH (10 mL) was stirred under a
H2 atmosphere for 16 h and filtered through a Celite plug. The
solvent was removed under reduced pressure, and the residue was
dissolved in CHCl3 (15 mL). To it was added bis(pyridine)iodonium
tetrafluoroborate (1.90 g, 5.1 mmol). The reaction mixture was
stirred at room temperature for 1 h, and the solvent was removed
under reduced pressure. The crude product was purified by column
chromatography on silica gel, eluting with hexanes-acetone (1:1)
General Procedure for the Synthesis of Acyloxymethyl or
Alkoxycarbonyloxymethyl Prodrugs of Phosphonic Acid 22c:
Di(pivaloyloxymethyl) [3,5-Dimethyl-4-(4′-hydroxy-3′-isopropyl-
benzyl)phenoxy]methylphosphonate (68). To a mixture of 22c (0.2
g, 0.5 mmol) and N,N-diisopropylethylamine (0.57 mL, 3.0 mmol)
in CH3CN (5 mL) at 0 °C was added pivaloyloxymethyl iodide48
(0.6 mL, 3.0 mmol). The reaction mixture was stirred at room
temperature for 16 h, and the solvent was removed under reduced
pressure. The crude product was purified by column chromatog-
raphy on silica gel, eluting with acetone-hexanes (1:3) to afford
1
68 as a white solid (0.22 g, 76%). H NMR (300 MHz, CD3OD):
δ 6.82 (d, J ) 2.1 Hz, 1H), 6.71 (s, 2H), 6.59 (d, J ) 7.8 Hz, 1H),
6.54 (dd, J ) 7.8, 2.1 Hz, 1H), 5.85-5.70 (m, 4H), 4.46 (d, J )
9.9 Hz, 2H), 3.90 (s, 2H), 3.22 (hpt, J ) 6.9 Hz, 1H), 2.22 (s, 6H),
1.22 (s, 18H), 1.14 (d, J ) 6.9 Hz, 6H). LC-MS m/z ) 593
[C31H45O9P + H]+. Anal. (C31H45O9P·0.3H2O) C, H.
Di(ethoxycarbonyloxymethyl) [3,5-Dimethyl-4-(4′-hydroxy-3′-
isopropylbenzyl)phenoxy]methylphosphonate (69). 1H NMR (300
MHz, DMSO-d6): δ 9.01 (s, 1H), 6.86 (d, J ) 2.1 Hz, 1H), 6.73
(s, 2H), 6.62 (d, J ) 8.1 Hz, 1H), 6.46 (dd, J ) 8.1, 2.1 Hz, 1H),
5.72 (s, 2H), 5.68 (s, 2H), 4.49 (d, J ) 7.5 Hz, 2H), 4.16 (q, J )
6.9 Hz, 4H), 3.82 (s, 2H), 3.14 (hpt, J ) 6.9 Hz, 1H), 2.18 (s, 6H),
1.20 (t, J ) 6.9 Hz, 6H), 1.11 (d, J ) 6.9 Hz, 6H). LC-MS m/z
) 569 [C27H37O11P + H]+. Anal. (C27H37O11P) C, H.
Di(isopropoxycarbonyloxymethyl) [3,5-Dimethyl-4-(4′-hydroxy-
3′-isopropylbenzyl)phenoxy]methylphosphonate (70). 1H NMR
(300 MHz, DMSO-d6): δ 9.06 (s, 1H), 6.86 (d, J ) 2.1 Hz, 1H),
6.73 (s, 2H), 6.62 (d, J ) 7.8 Hz, 1H), 6.45 (dd, J ) 7.8, 2.1 Hz,
1H), 5.71 (s, 2H), 5.67 (s, 2H), 4.80 (hpt, J ) 6.1 Hz, 2H), 4.48
(d, J ) 9.9 Hz, 2H), 3.82 (s, 2H), 3.14 (hpt, J ) 6.9 Hz, 1H), 2.18
(s, 6H), 1.23 (d, J ) 6.9 Hz, 6H), 1.21 (d, J ) 6.9 Hz, 6H), 1.11
(d, J ) 6.9 Hz, 6H). LC-MS m/z ) 597 [C29H41O11P + H]+. Anal.
(C29H41O11P) C, H.
1
to afford 9 as a yellow solid (1.30 g, 88%). H NMR (300 MHz,
CD3OD): δ 7.67 (s, 2 H), 7.13 (d, J ) 8.4 Hz, 1 H), 4.00-4.25
(m, 5 H), 3.00 (m, 1 H), 2.64 (m, 1 H), 1.38 (m, 6 H). LC-MS
m/z ) 626 [C17H26I2NO6P + H]+. Rf ) 0.70 (hexanes-acetone,
1:1).
Diethyl 1-tert-Butoxycarbonylamino-2-[4-(4′-tert-butyldimeth-
ylsilanyloxy)phenoxy-3,5-diiodophenyl]ethylphosphonate (10). To
a mixture of 9 (0.6 g, 0.96 mmol), 4-(tert-butyldimethylsiloxy)phe-
nylboronic acid (0.73 g, 2.89 mmol), Cu(OAc)2 (0.21 g, 1.16 mmol),
and 4 Å molecular sieves (1.20 g) in CH2Cl2 (8 mL) was added a
solution of pyridine (0.40 mL) and Et3N (0.70 mL). The reaction
mixture was stirred at room temperature for 48 h, filtered through
a Celite plug, and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel, eluting with
hexanes-acetone (3:1) to afford 10 as a white solid (0.48 g, 60%).
1H NMR (300 MHz, CD3OD): δ 7.64 (s, 2 H), 7.18 (d, J ) 8.4
Hz, 1 H), 6.64 (d, J ) 8.4 Hz, 1 H), 6.53 (d, J ) 8.4 Hz, 1 H),
6.38 (d, J ) 8.4 Hz, 1 H), 4.00 (m, 5 H), 2.90 (m, 1 H), 2.58 (m,
1 H), 1.20 (m, 6 H), 0.90 (m, 9 H), 0.03 (s, 3 H), 0.02 (s, 3 H).
LC-MS m/z ) 832 [C29H44I2NO7PSi + H]+. Rf ) 0.60
(hexanes-acetone, 7:3).
Di-(S-acetyl-2-thioethyl) [3,5-Dimethyl-4-(4′-hydroxy-3′-isopro-
pylbenzyl)phenoxy]methylphosphonate (71). A mixture of S-acetyl-
2-thioethanol (0.12 g, 0.96 mmol), 22c (0.10 g, 0.25 mmol), pyridine
(1 mL), and dicyclohexylcarbodiimide (0.14 g, 0.69 mmol) in DMF
(2.5 mL) was heated at 70 °C for 16 h. The reaction mixture was
cooled to room temperature and concentrated under reduced
pressure. The crude product was purified by column chromatog-
raphy on silica gel, eluting with ethyl acetate-hexanes (1:1) to
Diethyl 1-tert-Butoxycarbonylamino-2-[4-(4′-hydroxyphenoxy)-
3,5-diiodophenyl]ethylphosphonate (11). To a mixture of 10 (0.45
g, 0.54 mmol) in THF (6 mL) at 0 °C was added a solution of
TBAF (0.81 mL, 0.81 mmol, 1 M in THF). The reaction mixture
was stirred at room temperature for 20 min, and the solvent was
removed under reduced pressure. The crude product was purified
bycolumnchromatographyonsilicagel,elutingwithhexanes-acetone
1
1
afford 71 as an oil (0.09 g, 56%). H NMR (300 MHz, DMSO-
(1:1) to afford 11 as a white solid (0.24 g, 62%). H NMR (300
d6): δ 8.98 (s, 1H), 6.84 (d, J ) 1.8 Hz, 1H), 6.73 (s, 2H), 6.61 (d,
J ) 8.4 Hz, 1H), 6.44 (dd, J ) 8.4, 1.8 Hz, 1H), 4.42 (d, J ) 9.9
Hz, 2H), 4.16-4.11 (m, 4 H), 3.80 (s, 2H), 3.17-3.10 (m, 5H),
2.34 (s, 6H), 2.17 (s, 6H), 1.09 (d, J ) 6.9 Hz, 6H). LC-MS m/z
) 569 [C27H37O7PS2 + H]+. Anal. (C27H37O7PS2) C, H.
MHz, CD3OD): δ 7.74 (s, 2 H), 6.58 (d, J ) 8.4 Hz, 2 H), 6.45 (d,
J ) 8.4 Hz, 2 H), 4.12 (m, 5 H), 3.08 (m, 1 H), 2.64 (m, 1 H),
1.32 (m, 6 H). LC-MS m/z ) 618 [C18H22I2NO5P + H]+. Rf )
0.40 (hexanes-acetone, 1:1).
Diethyl 1-Amino-2-[3,5-diiodo-4-(4′-hydroxy-3-iodophenoxy)phe-
nyl]ethylphosphonate (12). A mixture of 11 (0.14 g, 0.20 mmol)
in 70% aqueous TFA (5 mL) was stirred at room temperature for
1 h, and the solvent was removed under reduced pressure. The
residue was dissolved in EtOH (4 mL) and cooled to 0 °C. To it
was added 40% aqueous MeNH2 (0.80 mL) followed by a solution
of KI (0.16 g, 0.96 mmol) and I2 (0.06 g, 0.23 mmol) in H2O (0.6
mL). The reaction mixture was stirred at 0 °C for 1 h, quenched
with H2O, and extracted with ethyl acetate (2 × 10 mL). The
combined organic layers were dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude product was purified
by column chromatography on silica gel, eluting with
MeOH-CH2Cl2 (1:24) to afford 12 as a yellow solid (0.10 g, 69%).
1H NMR (300 MHz, CD3OD): δ 7.85 (s, 2 H), 7.00 (d, J ) 5.2
Hz, 1 H), 6.74 (d, J ) 8.4 Hz, 1 H), 6.64 (dd, J ) 3.2, 8.4 Hz, 1
H), 4.18 (m, 5 H), 3.08 (m, 1 H), 2.78 (m, 1 H), 1.36 (m, 6 H). Rf
) 0.55 (MeOH-CH2Cl2, 1:24).
General Procedure for the Synthesis of Cis Cyclic 1-Aryl-1,3-
propanyl Prodrugs of Phosphonic Acid 22c: (2R,4S)-2-[(3,5-
Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)-phenoxy)methyl]-4-(3-
chlorophenyl)-2-oxido[1,3,2]dioxaphosphonane (72). To a mixture
of 22c (0.2 g, 0.55 mmol), (S)-1-(3-chlorophenyl)-1,3-propane diol
(0.31 g, 1.6 mmol), and pyridine (1 mL) in DMF (5 mL) at room
temperature was added 1,3-dicyclohexylcarbodiimide (0.34 g, 1.6
mmol). The reaction mixture was heated at 70 °C for 4 h, cooled
to room temperature, and filtered through a Celite plug. The solvent
was removed under reduced pressure and the crude product was
purified by column chromatography on silica gel, eluting with
CH2Cl2-MeOH (96:4) to afford the cis-prodrug 72 (0.06 g, 15%)
1
as a white solid: mp 77-82 °C. H NMR (300 MHz, DMSO-d6):
δ 8.97 (s, 1H), 7.47 (m, 1H), 7.38-7.31 (m, 3H), 6.82 (d, J ) 2.1
Hz, 1H), 6.73 (s, 2H), 6.59 (d, J ) 8.1 Hz, 1H), 6.43 (dd, J ) 8.1,
2.0 Hz, 1H), 5.73 (ddd, J ) 9.8, 3.7, 1.2 Hz, 1H), 4.61-4.50 (m,
1H), 4.45 (d, J ) 9.0 Hz, 2H), 4.45-4.35 (m, 1H), 3.78 (s, 2H),
3.08 (hpt, J ) 9.0 Hz, 1H), 2.30-2.10 (m, 2H), 2.14 (s, 6H), 1.07
(d, J ) 6.9 Hz, 6H). 13C NMR (75 MHz, DMSO-d6): δ 142.9 (d,
J ) 6.9 Hz), 156.2 (d, J ) 13.3 Hz), 152.7, 138.3, 134.3, 133.7,
131.2, 130.8, 130.2, 128.7, 126.0, 125.9, 125.3, 124.8, 115.2, 114.3,
78.4 (d, J ) 7.2 Hz), 66.9 (d, J ) 7.5 Hz), 61.7 (d, J ) 169.0 Hz),
33.6, 33.3 (d, J ) 6.6 Hz), 26.9, 22.9, 20.5. 32P NMR (121 MHz,
1-Amino-2-[3,5-diiodo-4-(4′-hydroxy-3′-iodophenoxy)]phenyleth-
ylphosphonic Acid (13). Deprotection of 12 with TMSBr as
1
described above afforded 13 as a yellow solid in 95% yield. H
NMR (300 MHz, CD3OD): δ 7.91 (s, 2 H), 7.02 (d, J ) 2.7 Hz, 1
H), 6.74 (d, J ) 8.4 Hz, 2 H), 6.64 (dd, J ) 3.0, 8.4 Hz, 1 H), 3.60
(m, 1 H), 2.92 (m, 1 H). LC-MS m/z ) 688 [C14H13I3NO5P +
H]+. Anal. (C14H13I3NO5P·1.0H2O·0.3HBr) C, H, N.

Phosphonic Acid TR Agonists
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22 7091
DMSO-d6): δ 29.5. LC-MS m/z ) 516 [C28H32ClO5P + H]+. Anal.
(C28H32ClO5P·0.2H2O) C, H.
temperature and concentrated under reduced pressure. The residue
was partitioned between EtOAc (50 mL) and aqueous NaHCO3
solution (100 mL). The organic layer was separated, washed with
brine, dried (Na2SO4), filtered, and concentrated under reduced
pressure. The crude product was purified by column chromatog-
raphy on silica gel, eluting with CH2Cl2-MeOH (95:5) to give 79
as an off-white foam (41.3 mg, 20%). 1H NMR (300 MHz, DMSO-
d6): δ 8.97 (s, 1H), 6.81 (s, 1H), 6.63 (s, 2H), 6.57 (d, J ) 8.4 Hz,
1H), 6.43 (d, J ) 7.8 Hz, 1 H), 4.82-4.70 (m, 2H), 4.15-4.00 (m,
2H), 4.00 (d, J ) 6.6 Hz, 2H), 3.78 (s, 2H), 3.75-3.58 (m, 4H),
3.11 (hpt, J ) 6.9 Hz, 1H), 2.15 (s, 6H), 1.16 (t, J ) 7.2 Hz, 6H),
1.07 (d, J ) 6.6 Hz, 6H). 31P NMR (121.5 MHz, DMSO-d6) δ
21.36. LC-MS m/z ) 535.3 [C27H39N2O7P + H]+. Anal.
(C27H39N2O7P). C, H, N.
Di-N-(L-1-ethoxycarbonylethylamino) [3,5-Dimethyl-4-(4′-hydroxy-
3′-isopropylbenzyl)phenoxy]methylphosphonamide (80). Yellow
solid (175 mg, 52%), mp 48-50 °C. 1H NMR (300 MHz, CDCl3):
δ 7.29 (s, 1H), 6.95 (s, 1H), 6.66 (s, 2H), 6.64 (d, J ) 8.4 Hz, 1H),
6.55 (d, J ) 7.8 Hz, 1 H), 5.10 (s, 1H), 4.30-4.1 (m, 6H), 3.93 (s,
2H), 3.45 (q, J ) 9.3 Hz, 2H), 3.20 (hpt, J ) 6.9 Hz, 1H), 2.24 (s,
6H), 1.46 (d, J ) 7.2 Hz, 6H), 1.28 (t, J ) 7.5 Hz, 6H), 1.24 (d,
J ) 6.9 Hz, 6H). 31P NMR (121.5 MHz, CDCl3) δ 96.08. LC-MS
m/z ) 563 [C29H43N2O7P + H]+. Anal. (C29H43N2O7P·0.5H2O)
C, H, N.
cis-2-[(3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy)-
methyl]-4-(4-chlorophenyl)-2-oxido[1,3,2]dioxaphosphonane (73).
Yellow solid, mp 77-80 °C. 1H NMR (300 MHz, CD3OD): δ
7.37-7.28 (m, 4H), 6.82 (d, J ) 1.8 Hz, 1H), 6.71 (s, 2H), 6.58
(d, J ) 8.4 Hz, 1H), 6.53 (dd, J ) 8.1, 1.8 Hz, 1H), 5.72 (br d, J
) 11.1 Hz, 1H), 4.75-4.63 (m, 1H), 4.59-4.42 (m, 3H), 3.90 (s,
2H), 3.20 (hpt, J ) 6.8 Hz, 1H), 2.50-2.30 (m, 2H), 2.20 (s, 6H),
1.12 (d, J ) 6.8 Hz, 6H). 31P NMR (121.5 MHz, CD3OD) δ 18.45.
LC-MS m/z ) 515 [C28H32ClO5P + H]+. Anal. (C28H32ClO5P·
0.1H2O·0.1CH2Cl2) C, H.
cis-2-[(3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy)-
methyl]-4-(3-bromophenyl)-2-oxido[1,3,2]dioxaphosphonane (74).
Yield 80 mg (21%), mp 70-75 °C. 1H NMR (300 MHz, DMSO-
d6): δ 8.98 (s, 1H), 7.63 (s, 1H), 7.53 (d, J ) 7.5 Hz, 1H),
7.40-7.28 (m, 2H), 6.84 (s, 1H), 6.75 (s, 2H), 6.60 (d, J ) 9.0
Hz, 1H), 6.45 (d, J ) 9.0 Hz, 1H), 5.74 (br d, J ) 12.0 Hz, 1H),
4.65-4.55 (m, 1H), 4.55-4.38 (m, 3H), 3.81 (s, 2H), 3.12 (hpt, J
) 6.9 Hz, 1H), 2.30-2.10 (m, 2H), 2.16 (s, 6 H), 1.09 (d, J ) 6.9
Hz, 6 H). 31P NMR (121.5 MHz, CD3OD) δ 15.45. LC-MS m/z
) 559, 561 [C28H32BrO5P + H]+. Anal. (C28H32BrO5P) C, H.
cis-2-[(3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy)-
methyl]-4-(3-fluorophenyl)-2-oxido[1,3,2]dioxaphosphonane (75).
1
Yield 130 mg (38%), mp 75-80 °C. H NMR (300 MHz, DMSO-
Di-N-(1-ethoxycarbonyl-1-methylethylamino)[3,5-dimethyl-4-(4′-
hydroxy-3′-isopropylbenzyl)]phenoxy]methylphosphonamide (81).
1H NMR (300 MHz, CD3OD): δ 6.85 (s, 1H), 6.75 (s, 2H), 6.61
(d, J ) 8.4 Hz, 1H), 6.54 (dd, J ) 8.4, 1.8 Hz, 1H), 4.25-4.15
(m, 6H), 4.00 (d, J ) 6.6 Hz, 2H), 3.93 (s, 2H), 3.12 (hpt, J ) 6.9
Hz, 1H), 2.24 (s, 6H), 1.61 (s, 3H), 1.56 (s, 3H), 1.30 (t, J ) 7.1
Hz, 6H), 1.16 (d, J ) 6.6 Hz, 6H). 31P NMR (121.5 MHz, CD3OD)
δ 92.88. LC-MS m/z ) 591 [C31H47N2O7P + H]+. Anal.
(C31H47N2O7P) C, H, N.
d6): δ 8.98 (s, 1H), 7.41-7.36 (m, 1H), 7.24-7.14 (m, 3H), 6.83 (s,
1H), 6.74 (s, 2H), 6.60 (d, J ) 8.1 Hz, 1H), 6.45 (d, J ) 8.1 Hz, 1H),
5.75 (br d, J ) 10.8 Hz, 1H), 4.60-4.50 (m, 1H), 4.50-4.41 (m,
3H), 3.80 (s, 2H), 3.12 (hpt, J ) 6.9 Hz, 1H), 2.27-2.29 (m, 1H),
2.16 (s, 6H), 1.09 (d, J ) 6.9 Hz, 6H). LC-MS m/z ) 499
[C28H32FO5P + H]+. Anal. (C28H32FO5P·0.2EtOAc) C, H.
cis-2-[(3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy)m-
ethyl]-4-(3,5-dichlorophenyl)-2-oxido[1,3,2]dioxaphosphonane (76).
1
Yield 50%, mp 79-81 °C. H NMR (300 MHz, CD3OD): δ 7.44
Di-N-(L-1-ethoxycarbonyl-2-methylpropylamino) [3,5-Dimethyl-
4-(3′ -isopropyl-4′ -hydroxybenzyl)phenoxy]meth-
ylphosphonamide (82). Mp 52-55 °C. 1H NMR (300 MHz,
CDCl3): δ 7.20 (s, 2H), 6.84 (d, J ) 1.8 Hz, 1H), 6.55 (s, 2H),
6.52 (d, J ) 7.2 Hz, 1H), 6.42 (dd, J ) 7.2, 1.8 Hz, 1H), 5.10 (b
s, 1H), 4.20-4.02 (m, 6H), 3.80 (s, 2 H), 3.35-3.22 (m, 1H),
3.20-3.08 (s, 1H), 3.11 (hpt, J ) 6.9 Hz, 1H), 2.13 (s, 6H),
2.15-2.00 (m, 2H), 1.20-1.09 (m, 12H), 0.95 (t, J ) 6.9 Hz, 6H),
0.81 (t, J ) 6.9 Hz, 6H). 31P NMR (121.5 MHz, CDCl3) δ 95.11.
(s, 2H), 6.84 (d, J ) 1.8 Hz, 1H), 6.76 (s, 2H), 6.61 (d, J ) 8.4
Hz, 1H), 6.55 (dd, J ) 8.4, 1.8 Hz, 1H), 5.77 (br d, J ) 10.5 Hz,
1H), 4.80-4.65 (m, 1H), 4.63-4.55 (m, 1H), 4.54 (d, J ) 9.3 Hz,
2H), 3.93 (s, 2H), 3.23 (hpt, J ) 6.8 Hz, 1H), 2.50-2.30 (m, 2H),
2.24 (s, 6H), 1.15 (d, J ) 6.8 Hz, 6H). 31P NMR (121.5 MHz,
CD3OD) δ 16.78. LC-MS m/z ) 549 [C28H31Cl2O5P + H]+. Anal.
(C28H31Cl2O5P·0.1H2O) C, H, Cl.
cis-2-[(3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy)-
methyl]-4-(pyrid-4-yl)-2-oxido[1,3,2]dioxaphosphonane (77). Yield
LC-MS m/z
)
619 [C33H51N2O7P
(C33H51N2O7P·0.75H2O) C, H, N.
+
H]+. Anal.
1
20%, mp 75-77 °C. H NMR (300 MHz, CD3OD): δ 8.55-8.50
(m, 2H), 7.50-7.43 (m, 2H), 6.85 (d, J ) 1.8 Hz, 1H), 6.72 (s,
2H), 6.61 (d, J ) 8.4 Hz, 1H), 6.54 (dd, J ) 8.4, 1.8 Hz, 1H),
5.90-5.80 (m, 1H), 4.83-4.50 (m, 3H), 3.93 (s, 2H), 3.23 (hpt, J
) 6.8 Hz, 1H), 2.50-2.30 (m, 2H), 2.23 (s, 6H), 1.15 (d, J ) 6.8
Hz, 6H). 31P NMR (121.5 MHz, CD3OD) δ 17.29. LC-MS m/z
) 482 [C27H32NO5P + H]+. Anal. (C27H32NO5P) C, H, N.
cis-2-[(3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy)-
methyl]-4-(pyrid-3-yl)-2-oxido[1,3,2]dioxaphosphonane (78). Yield
108 mg (50%), mp 75-78 °C. 1H NMR (300 MHz, CD3OD): δ 8.67
(s, 1H), 8.60-8.50 (m, 1H), 7.88 (d, J ) 8.4 Hz, 1H), 7.50-7.38 (m,
1H), 6.86 (d, J ) 1.8 Hz, 1H), 6.75 (s, 2H), 6.62 (d, J ) 8.4 Hz, 1H),
6.53 (dd, J ) 8.4, 1.8 Hz, 1H), 5.88 (br d, J ) 11.4 Hz, 1H), 4.83-4.50
(m, 3H), 3.93 (s, 2H), 3.23 (hpt, J ) 6.8 Hz, 1H), 2.60-2.42 (m,
Di-N-(L-1-ethoxycarbonyl-2-phenylethylamino) [3,5-Dimethyl-
4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy]methylphospho-
namide (83). Mp 60-63 °C. H NMR (300 MHz, DMSO-d6): δ
9.00 (s, 1H), 7.30-7.15 (m, 10H), 6.84 (s, 1H), 6.63 ((d, J ) 8.1
Hz, 1H), 6.53 (s, 2H), 6.52 (dd, J ) 8.1, 1.8 Hz, 1H), 4.75 (t, 1H),
4.38 (t, 1H), 4.10-3.90 (m, 6H), 3.95 (s, 2H), 3.63 (d, J ) 9.0 Hz,
2H), 3.15 (hpt, J ) 6.9 Hz, 1H), 3.00-2.75 (m, 4H), 2.19 (s, 6H),
1.20-1.05 (m, 12H). LC-MS m/z ) 715 [C41H51N2O7P + H]+.
Anal. (C41H51N2O7P·0.4H2O). C, H, N.
TR Binding Affinity Measurements. Recombinant TRR/RXRR
and TRꢀ/RXRR heterodimers were generated by means of a
baculovirus expression system (Invitrogen, Carlsbad, CA). cDNAs
encoding TRR1 (IMAGE, 2961613) and TRꢀ1 (ATCC ID, 67244)
were purchased from the American Type Culture Collection
(Manassas, VA). cDNA for RXRR was purchased from Stratagene
(San Diego, CA). The Bac-to-Bac baculovirus expression system
was purchased from Invitrogen (Carlsbad, CA) and used to
coexpress a His-tagged ligand binding domain of either TRR1 or
TRꢀ1 with RXRR. A receptor binding assay using scintillation
proximity assay (SPA) bead methodology was established using
copper coated SPA beads (Amersham, Piscataway, NJ) and
validated by characterizing the specificity and saturability of [125I]T3
binding. Displacement curves for compounds of interest were
generated and analyzed using a four-parameter logistic curve fit
model (SigmaPlot, Systat, CA).
1
1H), 2.35-2.20 (m, 1H), 2.23 (s, 6H), 1.15 (d, J ) 6.8 Hz, 6H). 31
P
NMR (121.5 MHz, CD3OD) δ 17.17. LC-MS m/z ) 482
[C27H32NO5P + H]+. Anal. (C27H32NO5P) C, H, N.
General Procedure for the Synthesis of Bis-amidate Prodrugs
of Phosphonic Acid 22c: Di-N-(ethoxycarbonylmethylamino) [3,5-
Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy]meth-
ylphosphonic Diamide (79). To a stirred solution of 22c (0.41 g,
1.11 mmol) and DMF (0.1 mL, 1.11 mmol) in dichloromethane
(5.6 mL) at 0 °C was added oxalyl chloride (0.38 mL, 4.4 mmol).
The reaction mixture was heated at reflux for 3 h, cooled to room
temperature, and concentrated under reduced pressure. To the
residue at 0 °C was added a solution of L-alanine ethyl ester (0.57
g, 4.3 mmol) and N,N-diisopropylethylamine (0.6 mL, 4.3 mmol)
in CH2Cl2. The reaction mixture was stirred for 14 h at room
Cholesterol Reducing Efficacy. Male Sprague-Dawley rats
were purchased from Harlan (Indianapolis, IN). The rats were fed

7092 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 22
Boyer et al.
(4) Metha, J. L., Ed.; Statins: Understanding Clinical Use; Saunders:
Philadelphia, PA, 2004.
(5) Clader, J. W. The discovery of ezetimibe: a view from outside the
a normal chow diet (Harlan 7001) supplemented with 1.5%
cholesterol and 0.5% cholic acid (w/w) for at least 10 days prior
to initiation of treatment. Plasma samples were obtained by tail
nick. Efficacy was calculated as the percentage of difference from
the total plasma cholesterol levels measured prior to dosing.
Compounds were suspended in water, and 0.1 M NaOH was added
dropwise until the compound was completely dissolved. All
compounds were dosed using a volume of 1 mL/kg. Dose-response
curves for compounds of interest were analyzed using a four-
parameter logistic curve fit model (SigmaPlot, Systat, CA).
Analysis of Mitochondrial Glycerol-3-phosphate Dehydroge-
nase Activity. Mitochondria were isolated by differential centrifuga-
tion following homogenization (1:4, w/v) in cold 0.23 M sucrose,
70 mM mannitol, 50 mM HEPES, pH 7.4, as described.59 mGPDH
was measured using a spectrophotometric method with 2-(4-
iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride as the
terminal electron acceptor.60 mGPDH activity was expressed as
[(units of mGPDH)/min]/(µg of protein) with 1 unit defined as the
amount of enzyme that converts 1.0 µmol of dihydroxyacetone
phosphate to R-glycerophosphate per minute at pH 7.4 at 25 °C.
Rat Pharmacokinetics for Prodrug 72. Three groups (n )
5/group) of catheterized male Sprague-Dawley rats (250-300 g, 6-8
weeks old) were dosed with compound 72 intravenously (iv) at 3 mg/
kg in 100% propylene glycol (PG) or orally (po) at 3 or 10 mg/kg in
100% polyethylene glycol (PEG)-400. Animals were fasted for 3 h
prior to oral administration and were refed 1 h after dosing. Animals
had free access to food prior to and during the iv evaluation. Blood
samples were taken predose and at 5, 20, and 40 min and 1, 1.5, 2, 3,
5, 8, 12, and 24 h following iv administration of compound 72 or at
0.5, 1, 2, 3, 4, 5, 6, 8, 12, and 24 h following oral administration.
Plasma was prepared from blood samples by centrifugation and
analyzed by liquid chromatography tandem mass spectrometry for
prodrug 72 and phosphonic acid 22c levels. The temporal profile of
prodrug 72 and phosphonic acid 22c concentrations in plasma was
analyzed by noncompartmental methods. The oral bioavailability of
prodrug 72 was calculated by comparison of the dose-normalized area
under the curve (AUC) values of the plasma concentrations of
compound 72 following oral administration with the AUC values of
compound 72 following iv administration. The relative oral bioavail-
ability of phosphonic acid 22c was estimated by dividing the plasma
AUC values of compound 22c after oral dosing of prodrug 72 by the
plasma AUC values of compound 22c following iv administration of
the prodrug 72.
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Acknowledgment. The authors thank Dr. Robert H.
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Supporting Information Available: Elemental analysis results
for compounds 13, 16, 22a-f, 27, 29, 32, 38a-c, 40, 45, 48,
57a-c, 61a,b, and 67-83 and mGPDH data. This material is
available free of charge via the Internet at http://pubs.acs.org.
(18) Chiellini, G.; Apriletti, J. W.; Yoshihara, H. A. I.; Baxter, J. D.; Ribeiro,
R. C. J.; Scanlan, T. S. A high-affinity subtype-selective agonist ligand
for the thyroid hormone receptor. Chem. Biol. 1998, 5 (6), 299–306.
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G.; Nguyen, N.-H.; Baxter, J. D.; Scanlan, T. S. Effects of the thyroid
hormone receptor agonist GC-1 on metabolic rate and cholesterol in
rats and primates: selective action relative to 3,5,3′-triido-L-tyronine.
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