Synthesis and biological activity of high-affinity retinoic acid receptor antagonists

Article abstract of DOI:10.1016/S0968-0896(99)00055-3

This article reports the synthesis and biological activity of new high affinity retinioic acid receptor (RAR) antagonists. The effect of introducing heteroatoms in the bicyclic ring system of the potent dihydronaphthalene RAR antagonist 8, and the variation of the pendant aromatic group on the ability of these compounds to function as RAR antagonists is discussed. The use of binding, transcriptional, and in vivo assays revealed that the 2,2-dimethylthiochromene analogue 59, and the 2,2-dimethylchromene derivative 85, were the most effective in blocking retinoid agonist induced activity. Copyright (C) 1999 Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(99)00055-3

Bioorganic & Medicinal Chemistry 7 (1999) 1321±1338
Synthesis and Biological Activity of High-Anity Retinoic Acid
Receptor Antagonists
Alan T. Johnson,* Liming Wang, Andrew M. Standeven, Maria Escobar
and Roshantha A. S. Chandraratna*
Retinoid Research, Departments of Chemistry and Biology, Allergan Inc., Irvine, CA 92623-9534, USA
Received 11 September 1998; accepted 2 December 1998
AbstractÐThis article reports the synthesis and biological activity of new high anity retinioic acid receptor (RAR) antagonists.
The e€ect of introducing heteroatoms in the bicyclic ring system of the potent dihydronaphthalene RAR antagonist 8, and the
variation of the pendant aromatic group on the ability of these compounds to function as RAR antagonists is discussed. The use of
binding, transcriptional, and in vivo assays revealed that the 2,2-dimethylthiochromene analogue 59, and the 2,2-dimethylchromene
derivative 85, were the most e€ective in blocking retinoid agonist induced activity. # 1999 Elsevier Science Ltd. All rights reserved.
Introduction
Various studies using these compounds have demon-
strated their potential as biological tools in under-
standing the mechanisms of retinoid action,9 and as
antidotes to retinoid induced toxicity.10 The present
clinical applications of nuclear receptor hormone
antagonists such as tamoxifen and RU 48611 suggests
that an RAR antagonist may also be of therapeutic
value. In addition, the recent ®nding that certain RAR
antagonists can function as inverse agonists12 provides
further interest in these molecules as it a€ords an
opportunity to explore a new area of RAR biology. In
this paper we present our recent ®ndings on the synth-
esis of heterocyclic analogues of 8 and comment on their
ability to function as RAR antagonists in cell based
assays and in vivo.
Recent advances in retinoid research underscore the
importance of these molecules in controlling normal
cellular processes.1 Upon binding to and activating
nuclear receptors, retinoids function as modulators of
gene transcription and thus play a key role in both
embryogenesis and the proper maintenance of various
cellular functions such as di€erentiation and prolifera-
tion. Two classes of retinoid receptors are currently
known. The retinoic acid receptors (RARa, b, and
g)2a±e have all-trans retinoic acid (ATRA) (1) as their
natural ligand, and the retinoid X-receptors (RXRa,
b, and g)2f,g for which 9-cis-retinoic acid (2) has been
proposed as the endogenous ligand3 (Chart 1). The
potential use of retinoid agonists in the treatment of
various human diseases, such as psoriasis,4 acne,5 can-
cer,6 and diabetes,7 continues to foster the search for
new classes of compounds with improved therapeutic
ratios.
Chemistry
The synthetic strategy used to prepare each series of
RAR antagonists of general structure A (Scheme 1)
follows our previously used route in the synthesis of the
dihydronaphthalene based RAR antagonist AGN
193109 (8)8i (Scheme 1). In each case, a ketone of the
general structure B served as the key intermediate in the
preparation of the ®nal retinoids by allowing the facile
addition of various aryl groups via a common enoltri-
¯ate. The aryl acid moieties D, are connected to the
bicyclic ring system C via an acetylene group using
standard palladium catalyzed coupling chemistry. Thus,
our initial focus was directed towards designing an e-
cient synthesis of thiochromanones 13 (Scheme 2) and
20±22 (Scheme 3), and the chromanones 28 and 29
(Scheme 4).
During the course of this work, a diverse group of
compounds 3±8 has emerged (Chart 1) that have been
shown to be antagonists of retinoid action mediated by
the RAR family of receptors.8 Compounds 3±6 are low
anity antagonists which required their use at con-
centrations in excess of 100- to 1000-fold of the natural
hormone ATRA to inhibit retinoid induced biological
activity. In contrast, retinoids 7 and 8 have been shown
to be potent RAR antagonists with binding anities
comparable to the natural ligand ATRA.
Key words: retinoic acid; receptor; antagonist; cutaneous; toxicity.
* Corresponding author. E-mail: johnson_alan@allergan.com
0968-0896/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(99)00055-3

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A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
Chart 1.
Scheme 1. Retrosynthetic analysis of chromene and thiochromene RAR antagonists.
The synthesis of thiochromanone 13 began with 4-bro-
mothiophenol (9) (Scheme 2). Treatment of 9 with aqu-
eous base followed by the addition of the potassium salt
of 3-bromopropionic acid a€orded 10 as a crystalline
solid in 75% yield.13 An intramolecular Friedel±Crafts
acylation reaction carried out in methanesulfonic acid
a€orded the desired thiochromanone 11 in excellent
yield.14 Coupling of 11 with trimethylsilylacetylene
using palladium catalysis at room temperature provided
12 in a modest 65% yield. Exposure of 12 to K2CO3 in
methanol followed by a second palladium catalyzed
coupling reaction of the intermediate terminal acetylene
with ethyl 4-iodo-benzoate a€orded the target com-
pound 13 in 29% overall yield from 9.
Our initial approach to thiochromanones 20±22 also
began with thiophenol 9 (Scheme 3). Heating 9 with 3-
methyl-2-butenoic acid and a catalytic amount of
piperidine a€orded 15 in good yield.15 However, all
attempts to ring close this carboxylic acid under stan-
dard Freidel±Crafts acylation conditions gave either
thioester 17 or a complex mixture of products. As a
result, we were forced to consider alternate routes to the
intermediate thiochromanone from which the following

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1323
Scheme 2. a(a) NaOH, BrCH2CH2CO2K, H2O, rt (75%); (b) CH3SO3H, 75 ꢀC, 1 h (90%); (c) HCCSiMe3, PdCl2(PPh3), CuI, DMF, Et2NH, rt
(65%); (d) K2CO3, MeOH, rt (96%); (e) 4-I-C6H4CO2Et, PdCl2(PPh3)2, CuI, THF, Et3N, 60 ꢀC (69%).
Scheme 3. (a) (CH3)2CˆCHCO2H, piperdine, 105 ꢀC, (15, 79%), (16, 82%); (b) H+; (c) (COCl)2, bz, rt; (d) SnCl4, CH2Cl2, 0 ꢀC, 2 h (78%); (e)
BBr3, CH2Cl2, 23 ꢀC (40%); (f) Tf2O, pyr 0 ꢀC to rt (47%); (g) TMSCꢁCH, Pd(PPh3)2Cl2, CuI, Et3N, 95 ꢀC (91%); (h) K2CO3, MeOH (99%); (i)
4-IC6H4CO2Et, Pd(PPh3)2Cl2, CuI, Et3N, (20, 72%), with 2-F-4-IC6H4CO2Et (21, 78%), with 6-I-C5H3N-3-CO2Et (22, 78%).
Scheme 4. (a) AcCl, Et3N, CH2Cl2, rt (83%); (b) AlCl3, 155 ꢀC, (72%); (c) acetone, piperidine, piperidinium tri¯uoroacetate, bz, 90 ꢀC, 44 h, (62%);
(d) TMSCꢁCH, Pd(PPH3)2Cl2, CuI, Et3N, 70 ꢀC, 24 h, (89%); (e) K2CO3, MeOH, (91%); (f) 4-IC6H4CO2Et, Pd(PPh3)2Cl2, CuI, Et3N, (28, 50%),
with 2-F-4-IC6H4CO2Et (29, 69%).
sequence proved successful. Thus, addition of 4-methoxy-
thiophenol (14) to 3-methyl-2-butenoic acid a€orded 16
which was then converted to the corresponding acid
chloride under standard conditions. Lewis acid medi-
ated cyclization of this intermediate proceeded without
incident to give 18 in good overall yield. Conversion of
methyl ether 18 to the corresponding phenol using an
16
excess of BBr3
followed by treatment with tri-
¯uoromethanesulfonic anhydride in pyridine17 a€orded
tri¯ate 19. Following the same protocol as described in

1324
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
Scheme 2, thiochromanone 20 was prepared from 19 in
good overall yield. In the same manner, the use of ethyl
2-¯uoro-4-iodobenzoate or ethyl 6-iodo-nicotinate in
place of ethyl 4-iodo-benzoate provided the o-¯uoro-
benzoate 21 and nicotinate 22 in good yield.
sodium enolate of 13 with the bis-tri¯imide reagent ®rst
reported by Comins.20 Palladium catalyzed coupling of
tri¯ate 30 with the organozinc reagent21 prepared from
the appropriate aryl halides a€orded thiochromenes 31±
35 in 40 to 94% yield. The required free carboxylic acids
36±40 were then prepared in good yield using standard
base hydrolysis conditions. Following the same syn-
thetic sequence, the 2,2-dimethylthiochromene deriva-
tives 57±69, and the 2,2-dimethylchomene analogues
79±85, were prepared as shown in Schemes 6 and 7.
The synthesis of the chromanone analogues 28 and 29
(Scheme 4) was based in part on a procedure to the
known 6-bromochromanone 26.18 Thus, acylation of
phenol 23 with acetyl chloride followed by Fries rear-
rangement of ester 24 a€orded the disubstituted acet-
ophenone 25 in 62% yield. Following the published
report, 25 was re¯uxed with an excess of acetone in the
presence of piperidine. To our surprise ketone 25 was
recovered unchanged. In an e€ort to facilitate this aldol
process19 a catalytic amount of piperidinium tri-
¯uoroacetate was added to the reaction mixture. This
change produced the desired chromanone 26 in 60%
yield. The use of weaker acids such as NH4OAc or
piperidinium acetate also gave the desired product but
in lower yields. One explanation for the observed dis-
crepancy with the published procedure is that in our
case ketone 25 was puri®ed by recrystallization prior to
the condensation step. The use of 25 directly from the
Fries rearrangement step may have retained some HCl
and thus the production of 26 was a result of catalysis
by piperidinium hydrochloride. Having secured a route
to bromochromane 26, the standard sequence of palla-
dium catalyzed coupling reactions described above
a€orded chromanones 28 and 29 in good overall yield.
Results and Discussion
The carboxylic acids prepared above were analyzed for
retinoid activity by testing in RAR and RXR binding
and transactivation assays. None of the compounds had
any detectable binding anity for the RXRs and were
also transcriptionally inactive at all three RXR sub-
types. All of the compounds tested lacked transcrip-
tional activity but displayed high anity for the RARs.
In general, the data in Table 1 indicate that all of the
retinoids bind to RARb with anities similar to the
natural ligand ATRA. In addition, these data also indi-
cate that the analogues bearing a 4-methyl- or 4-ethyl-
phenyl group have the highest anities for the three
RAR subtypes.
Preparation of the 4-aryl substituted thiochromene
antagonists was carried out using the synthetic sequence
outlined in Scheme 5. Conversion of ketone 13 to vinyl
tri¯ate 30 was readily accomplished by quenching the
Scheme 6. (a) NaN(TMS)2, THF, 5-Cl-2-NTf2-pyr, 78 ꢀC to 0 ꢀC,
(41, 61%), (42, 71%),(43, 87%); (b) ArZnCl, Pd(PPh3)4 THF, 50 ꢀC
(44±52, 16±96%), (53, 79%), (54, 86%), (55, 76%), (56, 83%); (c)
NaOH, THF, EtOH, H2O (57±65, 54±93%), (66, 83%), (67, 86%), 68
(81%), 69 (96%).
Scheme 5. (a) NaN(TMS)2, THF, 5-Cl-2-NTf2-pyr, 78 ꢀC to 0ꢀC
(69%); (b) ArZnCl, Pd(PPh3)4, THF, 50 ꢀC, (31±35, 40±94%); (c)
NaOH, THF, EtOH, H2O, (36±40, 78±85%).

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1325
The binding data for the 2,2-dimethylchromene analo-
gues 79±83, appears closer in pro®le to the correspond-
ing thiochromenes 36±40 as compared to the 2,2-
dimethylthiochromenes 57±61. Although the same
trends in the anity of the ligand for RARa and RARg
are observed with a change in alkyl substitution, they
appear less pronounced in this series. Thus, the di€er-
ence in C±O versus C±S bond lengths (1.4 A versus 1.8
A) appears to have placed the gem-dimethyl groups of
the chromenes in a slightly less favorable position for
interaction with the binding pocket of RARa and
RARg relative to the thiochromene analogues.
Previous work from these laboratories22 indicated that
the presence of a ¯uorine atom ortho- to the carboxyl
group can increase ligand binding to all three receptor
subtypes. However, this modi®cation when applied to
the present series of compounds resulted in no sig-
ni®cant change in Kd values relative to the parent
antagonists (compare 66 versus 58, 67 versus 59, 84
versus 80, and 85 versus 81).
To determine if the compounds listed in Table 1 would
function as antagonists in vitro, they were tested for
their ability to inhibit the transcriptional activity of the
potent RAR agonist TTNPB. Using a constant dose of
TTNPB, an increasing concentration of test antagonist
was used to determine an IC50 value at each RAR sub-
type. The potency of each antagonist relative to AGN
193109 (8) was then determined from the observed IC50
values of the test compound at each RAR subtype and
the IC50 for 8 in the same experiment. The results of
these experiments indicate that all of the compounds
tested can function as RAR antagonists in vitro as
initially suggested from their ability to bind to the
RARs in the absence of transcriptional activity. Table 2
contains data for a subset of the antagonists listed in
Table 1. The lack of a correlation between the observed
potencies and Kd values is attributed to the di€erent
experimental conditions used in the binding and trans-
activation assays.23 In general, we observed that only
when the di€erence in Kd values between 8 and the test
compound was greater than 10-fold would the relative
potency of the antagonist under study fall below a value
of one. This is exempli®ed by retinoid 38 where a 16-
fold di€erence in Kd values at RARg results in a relative
potency of 0.3 (Table 2). Although the resolution of this
assay is low, these data do show that each of these
compounds can compete with an RAR agonist in bind-
ing and activation of the RARs.
Scheme 7. (a) NaN(TMS)2, THF, 5-Cl-2-NTf2-pyr, 78 ꢀC to 0 ꢀC,
(70, 64%), (71, 58%); (b) ArZnCl, Pd(PPh3)4, THF, 50 ꢀC (72±76, 59±
92%), (77, 62%), (78, 79%), (c) NaOH, THF, EtOH, H2O, (79±83,
74±85%), (84, 94%), (85, 91%).
The thiochromene analogues 36±40 display the lowest
anity of the present set of compounds for RARg,
having Kd values 15- to 38-fold lower than the value for
AGN 193109 (8). In this same group of compounds, the
anity for RARa increases upon going from the phenyl
analogue 36, to the 4-methyl and 4-ethyl derivatives 37
and 38, but then decreases with an increase in size of the
4-alkyl groups as observed with 39 and 40.
The e€ect of introducing a gem-dimethyl group at C-2
of the thiochromene ring system was also explored. The
resulting 2,2-dimethylthiochromene analogues 57±61,
were found to bind with high anity to all three RARs,
displaying an 8 to 18-fold increase in anity at RARa
and an 8 to 30-fold increase at RARg relative to the des-
methyl analogues 36±40. The anity to RARb was also
increased although to a lesser extent. In this same series,
the use of heteroaromatic substituents such as pyridyl
and thienyl in place of a phenyl group at C-4 62±65,
showed little or no change in binding anity relative to
the 4-phenyl analogues. In contrast, replacement of the
benzoic acid moiety with the nicotinic acid group to give
68 and 69 proved detrimental to binding at RARa
resulting in an 11- to 23-fold drop in anity at this
RAR subtype while anity to RARb and RARg was
retained.
In a recent publication we presented in vivo evidence for
the potential of using RAR antagonists in the preven-
tion and treatment of retinoid induced toxicity.10 Fol-
lowing the same protocol, compounds from the present
set of RAR antagonists were tested for their ability to
inhibit topical toxicity induced by TTNPB. The data in
Table 3 shows the results of these experiments for a
subset of the compounds discussed above, along with
data for compound 8. At one half the concentration of
the RAR agonist, two of the antagonists, 59 and 85,
along with the reference compound 8, display very sig-
ni®cant inhibition of retinoid induced toxicity. At these

1326
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
Table 1. Binding anities for chromene and thiochromene RAR antagonists and reference compoundsa
RARa
b
Compound
X
Z
Ar
R1
R2
a
g
ATRA (1)
TTNPBb
8
15‹25
72‹37
17‹5
143‹46
27‹9
28‹8
124‹8
130‹42
8‹3
4‹2
3‹2
7‹3
13‹4
4‹1
12‹3
6‹2
19‹2
2‹0
4‹1
45‹5
70‹1
36‹1
14‹1
12‹3
16‹3
72‹4
14‹6
5‹1
13‹3
5‹2
7‹3
25‹10
4‹1
3‹1
9‹1
7‹3
5‹1
2‹1
2‹1
2‹1
4‹2
2‹0
6‹3
2‹0
5‹1
2‹1
10‹7
6‹4
4‹1
11‹3
5‹1
3‹0
8‹3
9‹4
6‹3
2‹0
18‹1
26‹20
7‹1
CMe2
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
4-Me-C6H5-
C6H5-
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
36
37
38
39
40
57
58
59
60
61
62
63
64
65
66
67
68
69
79
80
81
82
83
84
85
380‹199
116‹33
115‹33
297‹31
155‹26
13‹2
10‹3
5‹1
10‹3
20‹3
17‹4
18‹1
17‹7
57‹28
3‹1
4‹1
5‹1
9‹1
49‹2
14‹0
24‹4
39‹1
108‹13
28‹8
16‹4
4-Me-C6H5-
4-Et-C6H5-
4-iPr-C6H5-
4-tBu-C6H5-
C6H5-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
CH3-
4-Me-C6H5-
4-Et-C6H5-
4-iPr-C6H5-
4-tBu-C6H5-
6-Me-3-C5H3N-
5-Me-2-C4H2S-
5-ET-2-C4H2S-
5-tBu-2-C4H2S-
4-Me-C6H5-
4-Et-C6H5-
4-Me-C6H5-
4-Et-C6H5-
C6H5-
4-Me-C6H5-
4-Et-C6H5-
4-iPr-C6H5-
4-tBu-C6H5-
4-Me-C6H5-
4-Et-C6H5-
F
S
S
H
H
H
H
H
H
H
F
N
O
O
O
O
O
O
O
CH
CH
CH
CH
CH
CH
CH
F
aKd+SEM (nM).
bTTNPB=(Ro 13-7410), (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8,-tetramethyl-2-naphthyl)propen-1-yl]benzoic acid.
Table 2. Relative potencya and Kd valuesb of selected RAR
antagonists in the inhibition of transcriptional activity by the RAR
agonist TTNPB
in the observed toxicity with all the analogues, while at
an eightfold higher concentration these compounds
appear to o€er complete protection from retinoid ago-
nist induced toxicity.
RAR
b
Entry
a
g
38
1.1
28‹8
4.4
3‹1
0.3
115‹33
Conclusions
59
62
64
81
85
7.5
3‹2
6.5
2‹1
4.0
5‹1
The present series of compounds have been shown to
function as potent RAR antagonists in vitro and in
vivo. The introduction of heteroatoms into the basic
framework of AGN 193109 (8) has a€orded RAR
antagonists with similar or improved activity. The 4-
methyl- and 4-ethylphenyl analogues in the 2,2-di-
methylchromene and dimethylthiochromene series were
found to be the most potent of the compounds pre-
pared. In addition, the 2,2-dimethylthiochromene fra-
mework appears to be optimum for pan-RAR
antagonist activity showing no sensitivity to the size of
the 4-alkyl group of the aryl substituent located at C-4
of the heterocyclic ring system. The potential use of
these compounds as inhibitors of retinoid induced toxi-
city in vivo has also been clearly demonstrated by their
ability to block the activity of the potent RAR agonist
TTNPB. As a result, compound 59 (AGN 194310) is
9.3
4‹1
19.0
2‹0
3.3
17‹4
2.5
6‹2
5.5
2‹0
2.2
17‹7
4.4
12‹3
11.8
3‹0
2.4
24‹4
2.4
5‹1
12.2
2‹0
2.2
16‹4
aRelative Potency=IC50 (test compound)/IC50(8).
bKd values (nM) from Table 1.
same concentrations, the heterocyclic analogues 62 and
64 appear less ecient although they are still able to
block agonist activity. Using a twofold excess of the
antagonist relative to TTNPB results in ꢂ75% reduction

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1327
Table 3. Percent inhibitiona of TTNPB induced cutaneous toxicity at
with EtOAc. The combined organic layers were washed
with 2 N aqueous NaOH, H2O, and saturated aqueous
NaCl before being dried over MgSO4. The title com-
pound 2.26 g (67%), was isolated by column chromato-
various antagonist±agonist ratiosb
Ratio
2.0
Entry
0.5
8.0
1
graphy (3% EtOAc/hexanes) as a pale-yellow solid. H
8
72
79
32
44
71
85
84
76
78
86
98
94
90
84
92
NMR (300 MHz, CDCl3) d: 8.22 (1H, d, J=2.1 Hz),
7.48 (1H, dd, J=2.1, 8.3 Hz), 7.17 (1H, d, J=8.5 Hz),
3.24 (2H, t, J=6.4 Hz), 2.98 (2H, t, J=6.7 Hz).
59
62
64
85
6-(2-Trimethylsilylethynyl)-thiochroman-4-one (12).
A
aDetermined using the cutaneous toxicity scores10a for TTNPB with
vehicle control and in combination with the RAR antagonist.
bRatio=[antagonist]/[TTNPB].
solution of 11 1.00g (4.11 mmol) and 78.3 mg (0.41 mmol)
CuI in 15.0 mL THF and 6.0 mL Et2NH was sparged
with argon for 5 min. To the resulting solution was
added 2.0 mL (1.39 g, 14.2 mmol) of (trimethylsilyl)-
acetylene and 288.5 mg (0.41 mmol) of Pd(PPh3)2Cl2.
After stirring for 3 days at room temperature the mix-
ture was ®ltered through a pad of Celite and solids
washed with EtOAc. The ®ltrate was washed with H2O
and saturated aqueous NaCl before being dried over
MgSO4 and concentrated under reduced pressure. The
title compound 600.0 mg (55%), was isolated by column
chromatography (4% EtOAc/hexanes) as an orange oil.
1H NMR (300 MHz, CDCl3) d: 8.13 (1H, d, J=1.9 Hz),
7.36 (1H, dd, J=2.1, 8.2 Hz), 7.14 (1H, d, J=8.2 Hz),
3.19 (2H, d, J=6.3 Hz), 2.91 (2H, d, J=6.3 Hz), 0.21
(9H, s).
currently in pre-clinical development as a topical agent for
the treatment and prevention of the mucocutaneous toxi-
city produced by systemic retinoids such as Accutane2.
Experimental
General methods
1H NMR spectra were recorded using a Varian Gemini
300 spectrometer (300 MHz) and 13C NMR spectra
using a Varian XL 300 spectrometer (75.5 MHz) in the
solvent indicated. Elemental analyses were performed
by Robertson Microlit Laboratories, Inc., Madison NJ.
All ®nal retinoids were characterized by IR, low-resolu-
tion MS, 1H and 13C NMR.
Ethyl 4-[2-(4-oxo-thichroman-6-yl)ethynyl]benzoate (13).
A solution of 12 (600.0 mg, 2.25 mmol) and K2CO3
(100.0 mg, 0.72 mmol) in 15 mL of MeOH was stirred
overnight at room temperature. The solution was dilu-
ted with H2O and extracted with Et2O. The combined
organic layers were washed with H2O and saturated
aqueous NaCl before being dried over MgSO4.
Removal of the solvent under reduced pressure a€orded
405.0 mg (96%) of 6-ethynyl-thiochroman-4-one as an
orange solid which was used without further puri®ca-
tion. 1H NMR (300 MHz, CDCl3) d: 8.17 (1H, d,
J=1.8 Hz), 7.40 (1H, dd, J=1.8, 8.2 Hz), 7.19 (1H, d,
J=8.2 Hz), 3.22 (2H, t, J=6.3 Hz), 3.08 (1H, s), 2.94
(2H, t, J=6.3 Hz).
Thin-layer chromatography (TLC) was carried out
using Whattman silica gel 60 A plates (0.25 mm). Flash
chromatography was performed using E. Merck silica
gel 60 (230±400 mesh). All reactions were carried out
under a positive pressure of argon using reagent grade
or anhydrous solvents as received.
3-(4-Bromothiophenoxy)propionic acid (10). To a solution
of 1.44 g (35.7 mmol) of NaOH on 20.0 mL degassed
H2O (sparged with argon) was added 6.79 g (35.7 mmol)
of 4-bromothiophenol. The resulting mixture was stirred
at room temperature for 30 min. A second ¯ask was
charged with 2.26 g (16.3 mmol) of K2CO3 and 15.0 mL
degassed H2O. To this solution was added in small por-
tions 5.00 g (32.7 mmol) of 3-bromopropionic acid. The
resulting potassium carboxylate solution was added to
the sodium thiolate solution and the resulting mixture
stirred at room temperature for 48 h. The mixture was
®ltered and the aqueous extracted with benzene and the
organic layers discarded. The aqueous layer was acid-
i®ed with 10% aqueous HCl and extracted with EtOAc.
The combined organic layers were washed with saturated
aqueous NaCl, dried over MgSO4, and concentrated
under reduced pressure. The residual solid was recrys-
tallized from ether/hexanes to give 6.18g (72%) of the
title compound as o€-white crystals. 1H NMR (300MHz,
CDCl3) d: 7.43 (2H, d, J=8.4 Hz), 7.25 (2H, d, J=
8.4 Hz), 3.15 (2H, t, J=7.3 Hz), 2.68 (2H, t, J=7.3Hz).
A
solution 6-ethynyl-thiochroman-4-one (405.0 mg,
2.15 mmol) and ethyl 4-iodobenzoate (594.0 mg,
2.15 mmol) in 15 mL Et3N and 3 mL THF was sparged
with argon for 15 min. To this solution was added
Pd(PPh3)2Cl2 (503.0 mg, 0.72 mmol), and CuI (137.0 mg,
0.72 mmol). After stirring at room temperature for 20 h
the mixture was ®ltered through a pad of Celite using an
EtOAc wash. The combined organic layers were washed
with H2O and saturated aqueous NaCl before being
dried over MgSO4. Column chromatography (3%
EtOAc/hexanes) a€orded 500.0 mg (69%) of the title
1
compound as a pale-orange solid. H NMR (300 MHz,
acetone-d6) d: 8.15 (1H, d, J=2.0 Hz), 8.02 (2H, d,
J=8.5 Hz), 7.69 (2H, d, J=8.5 Hz), 7.61 (1H, dd, J=
2.1, 8.3 Hz), 7.40 (1H, d, J=8.2 Hz), 4.35 (2H, q, J=
7.1 Hz), 3.40 (2H, t, J=6.3 Hz), 2.96 (2H, t, J=6.3 Hz),
1.37 (3H, t, J=7.1 Hz).
6-Bromo-thiochroman-4-one (11). A solution of 3.63 g
(13.9 mmol) of 10 in 60 mL of methanesulfonic acid was
heated to 75 ꢀC for 1.5 h. After cooling to room tem-
perature the solution was diluted with H2O and extracted
Ethyl 4-[(4-trifuoromethylsulfonyloxy-(2H)-thiochromen-
6-yl)ethynyl] benzoate (30). To a solution of sodium
bis(trimethylsilyl)amide (221.9 mg, 1.21 mmol) in 3.0 mL

1328
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
THF at 78 ꢀC was added 13 (370.0 mg, 1.10 mmol) in
4.0 mL THF. After 30 min a solution of 2[N,N-bis(tri-
¯uormethylsulfonyl)amino]-5-chloropyridine (475.4 mg,
1.21 mmol) in 4.0 mL THF was added and the resulting
solution allowed to slowly warm to room temperature.
After 5 h the reaction was quenched by the addition of
saturated aqueous NH4Cl. The mixture was extracted
with EtOAc and the combined organic layers washed
with 5% aqueous NaOH, H2O, and saturated aqueous
NaCl before being dried over MgSO4. Removal of the
solvents under reduced pressure followed by column
chromatography (4% EtOAc/hexanes) of the residual
oil a€orded 81.0 mg (69%) of the title compound as a
0.28 mmol) and Pd(PPh3)4 (14.0 mg, 0.012 mmol) a€or-
ded 110.0 mg (93%) of the title compound as a colorless
solid. H NMR (300 MHz, acetone-d6) d: 7.98 (2H, d,
J=8.14 Hz), 7.57 (2H, d, J=8.4 Hz), 7.45±7.36 (2H, m),
7.29±7.16 (5H, m), 6.15 (1H, t, J=5.7 Hz), 4.31 (2H, q,
J=7.1 Hz), 3.50 (2H, d, J=5.7 Hz), 2.68 (2H, q,
J=7.5 Hz), 1.35 (3H, t, J=7.1 Hz),1.24 (3H, t, J=
7.5 Hz), Anal. calcd for C28H24O2S: C, 79.21; H, 5.70.
Found: C, 79.06; H, 5.48.
1
Ethyl 4-[(4-(4-(1-methylethyl)phenyl)-(2H)-thiochromen-
6-yl)ethynyl] benzoate (34). Following general procedure
A; 4-iso-propylbromobenzene (159.0 mg, 0.80 mmol), t-
BuLi (0.94 mL, 1.60 mmol), ZnCl2 (153.0 mg, 1.12 mmol),
30 (150.0 mg, 0.32 mmol) and Pd(PPh3)4 (24.0 mg,
0.021 mmol) a€orded 63.0 mg (45%) of the title com-
pound as a colorless solid. 1H NMR (300 MHz, CDCl3)
d: 7.98 (2H, d, J=8.4 Hz), 7.39±7.20 (7H, m), 6.07 (1H,
t, J=5.7 Hz), 4.36 (2H, q, J=6.8 Hz), 3.48 (2H, d,
J=5.7 Hz), 2.97 (1H, hept, J=6.8Hz), 1.57 (3H, t, J=
7.1 Hz), 1.32 (6H, d, J=6.8 Hz). Anal. calcd for C29H26
O2S: C, 79.42; H, 5.98. Found: C, 79.25; H, 6.07.
1
pale-yellow solid. H NMR (300 MHz, acetone-d6) d:
8.12 (2H, d, J=8.5 Hz), 7.66 (2H, d, J=8.5 Hz), 7.56
(1H, d, J=1.7 Hz), 7.49 (1H, dd, J=1.7, 8.1 Hz), 7.40
(1H, d, J=8.1 Hz), 6.33 (1H, t, J=5.7 Hz), 4.35 (2H, q,
J=7.1 Hz), 3.82 (2H, d, J=5.7 Hz), 1.37 (3H, t, J=
7.1 Hz).
General procedure A: ethyl 4-[(4-phenyl-(2H)-thio-
chroman-6-yl)ethynyl] benzoate (31). To a solution of
bromobenzene (101.0 mg, 0.63 mmol) in 2.0 mL THF at
78 ꢀC was added t-BuLi (0.74 mL of a 1.7 M solution
in pentane, 1.25 mmol). After stirring for 30 min a solu-
tion of ZnCl2 (119.0 mg, 0.88 mmol) in 2.0 mL THF was
added and the resulting pale-yellow solution warmed to
room temperature. Stirring for 40 min was followed by
the transfer of this solution to a second ¯ask containing
30 (120.0 mg, 0.25 mmol) and Pd(PPh3)4 (24.0 mg,
mmol) in 2.0 mL of THF. The resulting solution was
heated to 50 ꢀC for 2 h, cooled to room temperature and
quenched by the addition of saturated aqueous NH4Cl.
The mixture was extracted with EtOAc and the com-
bined organic layers washed with H2O and saturated
aqueous NaCl before being dried (MgSO4) and con-
centrated under reduced pressure. Column chromato-
graphy (3 to 5% EtOAc/hexanes) a€orded 40.0 mg
Ethyl 4-[(4-(4-(1,1-dimethylethyl)phenyl)-(2H)-thiochromen-
6-yl)ethynyl] benzoate (35). Following general procedure
A; 4-tert-butylbromobenzene (148.0 mg, 0.69 mmol),
t-BuLi (0.81 mL, 1.39 mmol), ZnCl2 (132.0 mg, 0.97 mmol),
30 (130.0 mg, 0.28 mmol) and Pd(PPh3)4 (24.0 mg,
0.021 mmol) a€orded 75.0 mg (65%) of the title
compound as a colorless solid. 1H NMR (300 MHz,
acetone-d6) d: 7.98 (2H, d, J=8.4 Hz), 7.57 (2H, d,
J=8.4 Hz), 7.49±7.39 (4H, m), 7.25±7.22 (2H, m), 7.17
(1H, d, J=1.7 hz), 6.16 (1H, t, J=5.7 Hz), 4.33 (2H, q,
J=7.1 Hz), 3.53 (2H, d, J=5.7 Hz), 1.34 (9H, s), 1.34
(3H, t, J=7.1 Hz). Anal. calcd for C30H28O2S: C, 79.43;
H, 6.05. Found: C, 79.61; H, 6.24.
General procedure B 4-[2-(4-phenyl-(2H)-thiochromen-6-
yl)-ethynyl]-benzoic acid (36). To a solution of 31
(27.7 mg, 0.07 mmol) in 2.0 mL THF and 2.0 mL EtOH
was added NaOH (80.0 mg, 2.0 mmol, 2.0 mL of a 1 M
aqueous solution). The resulting solution was heated to
40 ꢀC and stirred overnight. Upon cooling to room
temperature the reaction was acidi®ed with 10% aqu-
eous HCl and extracted with EtOAc. The combined
organic layers were washed with H2O, saturated aqu-
eous NaCl, and dried (Na2SO4) before removing the
solvent under reduced pressure. The residual solid was
recrystallized from CH3CN to give 20.0 mg (78%) of the
title compound as a pale-yellow solid. 1H NMR
(300 MHz, DMSO-d6) d: 7.90 (2H, d, J=8.4 Hz), 7.59
(2H, d, J=8.4 Hz), 7.45±7.37 (5H, m), 7.28±7.25 (2H,
m), 7.01 (1H, d, J=1.7 Hz), 6.15 (1H, t, J=5.7 Hz), 3.57
(2H, d, J=5.7 Hz). 13C NMR (75.5 MHz, DMSO-d6) d:
166.6, 139.7, 139.6, 135.4, 133.9, 131.4, 130.6, 130.5,
129.7, 129.4, 128.6, 128.1, 127.9, 126.3, 123.1, 118.5,
91.6, 88.6, 24.3.
1
(40%) of the title compound as a colorless solid. H
NMR (300 MHz, acetone-d6) d: 7.98 (2H, d, J=8.5 Hz),
7.57 (2H, d, J=8.5 Hz), 7.54±7.37 (5H, m), 7.32±7.29
(2H, m), 7.12 (1H, d, J=1.7 Hz), 6.17 (1H, t, J=5.7 Hz),
4.34 (2H, q, J=7.1 Hz), 3.56 (2H, d, J=5.7 Hz), 1.35
(3H, t, J=7.1 Hz). Anal. calcd for C26H20O2S: C, 78.76;
H, 5.08. Found: C, 78.66; H, 4.79.
Ethyl 4-[(4-(4-methylphenyl)-(2H)-thiochromen-6-yl)eth-
ynyl] benzoate (32). Following general procedure A; 4-
bromotoluene (120.8 mg, 0.70 mmol), t-BuLi (0.81 mL,
1.38 mmol), ZnCl2 (131.6 mg, 0.97 mmol), 30 (129.2 mg,
0.28 mmol) Pd(PPh3)4 (14.0 mg, 0.012 mmol) a€orded
45.0 mg (40%) of the title compound as a colorless
1
solid. H NMR (300 MHz, acetone-d6) d: 7.98 (2H, d,
J=8.3 Hz), 7.58 (2H, d, J=8.3 Hz), 7.44±7.38 (2H, m),
7.26±7.15 (5H, m), 6.14 (1H, t, J=5.8 Hz), 4.34 (2H, q,
J=7.1 Hz), 3.53 (2H, d, J=5.8 Hz), 2.37 (2H, s), 1.35
(3H, t, J=7.1 Hz). Anal. calcd for C27H22O2S: C, 78.9;
H, 5.40. Found: C, 78.75; H, 5.23.
4-[2-(4-(4-Methylphenyl)-(2H)-thiochromen-6-yl)-ethynyl]-
benzoic acid (37). Following general procedure B, 32
(29.0 mg, 0.07 mmol) in 2.0 mL THF and 2.0 mL EtOH
and NaOH (160.0 mg, 4.0 mmol, 2.0 mL of a 2 M aqueous
solution a€orded 22.0 mg (82%) of the title compound
Ethyl 4-[(4-ethylphenyl)-(2H)-thiochromen-6-yl)ethynyl]
benzoate (33). Following general procedure A; 4-ethyl-
bromobenzene (128.0 mg, 0.69 mmol), t-BuLi (0.81 mL,
1.38 mmol), ZnCl2 (131.6 mg, 0.97 mmol), 30 (129.2 mg,

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1329
1
as a pale-yellow solid. H NMR (300 MHz, DMSO-d6)
oil which upon standing in the freezer provided a crys-
talline solid. The title compound was isolated using a
pentane wash as pale-yellow crystals (27.33 g, 82%). H
NMR (300 MHz, CDCl3) d: 7.48 (2H, d, J=9.0 Hz),
6.89 (2H, d, J=8.9 Hz), 3.83 (3H, s), 2.54 (2H, s), 1.40
(6H, s).
d: 7.90 (2H, d, J=8.4 Hz), 7.59 (2H, d, J=8.4 Hz), 7.46±
7.40 (4H, m), 7.25±7.13 (4H, m), 7.02 (1H, d, J=1.7 Hz),
6.11 (1H, t, J=5.7 Hz), 3.54 (2H, d, J=5.7 Hz), 2.34
(3H, s); 13C NMR (75.5 MHz, DMSO-d6) d: 166.7,
139.5, 137.2, 136.8, 135.5, 134.5, 130.6, 130.5, 129.8,
129.5, 129.2, 128.5, 128.1, 126.4, 122.5, 118.5, 91.6, 88.6,
24.4, 20.8.
1
6-Methoxy-2,2-dimethyl-thiochroman-4-one (18). To a
solution of 3-(4-methoxy-phenylsulfanyl)-3-methyl-but-
yric acid (20.0 g, 83.2 mmol) in 250 mL of benzene at
room temperature was added a solution of oxalyl chlo-
ride (15.84 g, 124.8 mmol) in 10 mL of benzene over
30 min. After 4 h, the solution was washed with ice cold
5% aqueous NaOH (CAUTION: a large volume of gas
is released during this procedure), followed by ice cold
H2O, and ®nally saturated aqueous NaCl. The solution
was dried (Na2SO4) and concentrated under reduced
pressure to give the acyl chloride as a clear yellow oil.
This material was used without further puri®cation in
4-[2-(4-(4-Ethylphenyl)-(2H)-thiochromen-6-yl]-ethynyl)-
benzoic acid (38). Following general procedure B, 33
(90.0 mg, 0.21 mmol) in 3.0 mL THF and 3.0 mL EtOH
and NaOH (240.0 mg, 6.0 mmol, 3.0 mL of a 2 M aqu-
eous solution) a€orded 66.0 mg (79%) of the title com-
pound as a colorless solid. 1H NMR (300 MHz, DMSO-
d6) d: 7.89 (2H, d, J=8.3 Hz), 7.58 (2H, d, J=8.3 Hz),
7.46±7.37 2H, m)m 7.28±7.16 (4H, m), 7.03 (1H, d,
J=1.6 Hz), 6.13 (1H t, J=5.6Hz), 3.54 (2H, d, J=
5.6 Hz), 2.64 (2H, q, J=7.5 Hz), 1.21 (3H, t, J=7.5 Hz);
13C NMR (75.5 MHz, DMSO-d6) d: 166.6, 143.5, 139.5,
137.1, 135.5, 134.0, 131.5, 130.6, 130.4, 129.7, 129.4,
128.5, 128.1, 128.0, 126.4, 122.6, 118.5, 91.6, 88.6, 27.8,
24.3, 15.3.
1
the next step. H NMR (300 MHz, CDCl3) d: 7.45 (2H,
d, J=8.8 Hz), 6.90 (2H, d, J=8.8 Hz), 3.84 (3H, s), 3.12
(2H, s), 1.41 (6H, s).
To a solution of the acyl chloride (21.5 g, 83.2 mmol) in
250 mL of CH2Cl2 at 0 ꢀC was added dropwise a solu-
tion of SnCl4 (21.7 g, 83.2 mmol) in 30 mL of CH2Cl2.
After 2 h the reaction was quenched by the slow addition
of 150 mL H2O. The organic layer was washed with 1 M
aqueous HCl, 5% aqueous NaOH, H2O, and ®nally
saturated aqueous NaCl before being dried over
MgSO4. Concentration under reduced pressure and
vacuum distillation of the residual oil (bulb-to-bulb,
125±135 ꢀC, 5 mm/Hg) a€orded 14.48 g (78%) of the
4-[2-(4-(4-(1-Methylethyl)phenyl)-(2H)-thiochromen-6-yl)-
ethynyl]-benzoic acid (39). Following general procedure
B, 34 (44.0 mg, 0.10 mmol) in 3.0 mL THF and 3.0 mL
EtOH and NaOH (120.0 mg, 3.0 mmol, 3.0 mL of a 1 M
aqueous solution) a€orded 35.0 mg (85%) of the title
compound as a colorless solid. 1H NMR (300 MHz,
DMSO-d6) d: 7.90 (2H, d, J=8.3 Hz), 7.58 (2H, d,
J=8.3 Hz), 7.47±7.17 (6H, m), 7.04 1H, d, J=1.7 Hz),
6.13 (1H, t, J=5.7 Hz), 3.54 (2H, d, J=5.7 Hz), 2.92
(1H, hept., J=6.8 Hz), 1.23 (6H, d, J=6.8 Hz); 13C
NMR (75.5 MHz, DMSO-d6) d: 166.5, 148.0, 139.4,
137.1, 135.5, 133.9, 131.4, 130.6, 130.4, 129.6, 129.4,
128.5, 128.0, 126.5, 126.3, 122.6, 118.4, 91.5, 88.5, 33.0,
24.3, 23.7.
title compound as
a
pale-yellow oil. 1H NMR
(300 MHz, CDCl3) d: 7.62 (1H, d, J=2.9 Hz), 7.14 (1H,
d, J=8.6 Hz), 7.03 (1H, dd, J=2.8, 8.3 Hz), 3.83 (3H,
s), 2.87 (2H, s), 1.46 (6H, s).
2,2-Dimethyl-4-oxo-thiochroman-6-yl tri¯uoromethane-
sulfonate (19). To a solution of 6-methoxy-2,2-di-
methyl-thiochroman-4-one (6.0 g, 27 mmol) in 50 mL
CH2Cl2 cooled to 23 ꢀC was added BBr3 (20.0 g,
80.0 mmol; 80.0 mL of a 1 M solution in CH2Cl2) over a
20 min period. After stirring for 5 h at 23 ꢀC the solu-
tion was cooled to 78 ꢀC and quenched by the slow
addition of 50 mL of H2O. Upon warming to room
temperature the aqueous layer was extracted with
CH2Cl2 and the combined organic layers washed with
saturated aqueous NaHCO3, H2O, and saturated aqu-
eous NaCl before being dried over MgSO4. Removal of
the solvents under reduced pressure gave a green-brown
solid which upon recrystalization (Et2O/hexanes) a€or-
ded 2.25 g (40%) of the intermediate phenol as a light
4-[2-(4-(4-(1,1-Dimethylethyl)phenyl)-(2H)-thiochromen-
6-yl)-ethynyl]-benzoic acid (40). Following general pro-
cedure B, 35 (50.0 mg, 0.11 mmol) in 2.0 mL THF and
2.0 mL EtOH and NaOH (160.0 mg, 4.0 mmol, 2.0 mL
of a 2 M aqueous solution) a€orded 38.0 mg (81%) of
the title compound as an o€-white solid. 1H NMR
(300 MHz, DMSO-d6) d: 7.90 (2H, d, J=8.2 Hz), 7.58
(2H, d, J=8.2 Hz), 7.47±7.38 (4H, m), 7.21±7.18 (2H,
m), 7.05 (1H, s), 6.13 (1H, t, J=5.7 Hz), 3.54 (2H, d,
J=5.7 Hz), 1.31 (9H, s); 13C NMR (75.5 MHz, DMSO-
d6) d: 166.7, 150.3, 139.4, 136.8, 135.5, 134.0, 131.4,
130.7, 129.6, 129.4, 128.3, 128.1, 126.3, 125.4, 122.7,
118.5, 91.6, 88.6, 34.3, 31.1, 24.3.
1
3-(4-Methoxy-phenylsulfanyl)-3-methyl-butyric acid (16).
A heavy-walled screw cap tube was charged with 3-
methyl-2-butenoic acid (13.86 g, 138.4 mmol), 4-meth-
oxy thiophenol (20.0 g, 138.4 mmol), and piperidine
(3.45 g, 41.6 mmol). This mixture was heated to 105 ꢀC
for 32 h, cooled to room temperature and dissolved in
EtOAc (700 mL). The resulting solution was washed
with 1 M aqueous HCl, H2O, and saturated aqueous
NaCl before being dried over Nac2SO4. Concentration
of the dry solution under reduced pressure a€orded an
brown solid. H NMR (300 MHz, CDCl3) d: 7.63 (1H,
d, J=2.8 Hz), 7.15 (1H, d, J=8.5 Hz), 7.01 (1H, dd,
J=2.8, 8.5 Hz), 2.87 (2H, s), 1.46 (6H, s).
To a solution of the phenol (165.0 mg, 0.79 mmol) in
5.0 mL of anhydrous pyridine at 0 ꢀC was added tri-
¯uoromethanesulfonic anhydride (245.0 mg, 0.87mmol).
After 4 h at 0 ꢀC the solution was concentrated and the
residual oil dissolved in Et2O, washed with H2O fol-
lowed by saturated aqueous NaCl, and dried over

1330
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
MgSO4. Removal of the solvents under reduced pres-
sure and column chromatography (5% EtOAc/hexanes)
a€orded 126.0 mg (47%) of the title compound as a
colorless solid. 1H NMR (300 MHz, CDCl3) d: 7.97
(1H, s), 7.32 (2H, s), 2.90 (2H, s), 1.49 (6H, s).
for an additional 10 min with argon, the solution was
stirred overnight at room temperature. The reaction
mixture was ®ltered through a pad of Celite using an
Et2O wash. Concentration of the ®ltrate under reduced
pressure followed by column chromatography (5%
EtOAc/hexanes) of the residual solid a€orded 1.8 g
1
Ethyl 4-[(2,2-dimethyl-4-oxo-thiochroman-6-yl)ethynyl]-
benzoate (20). A solution of 19 (2.88 g, 8.50 mmol) in
10 mL Et3N and 20.0 mL DMF was sparged with argon
for 10 min. To this solution was added trimethylsilyl-
acetylene (4.15 g, 42.0 mmol) and bis(triphenylphos-
phine)-palladium(II) chloride (298.0 mg, 0.425 mmol).
The solution was heated to 95 ꢀC for 5 h, cooled to
room temperature, and diluted with H2O. Extraction
with EtOAc was followed by washing the combined
organic layers with H2O and saturated aqueous NaCl
and drying over MgSO4. Concentration of the dry
solution under reduced pressure and isolation of the
product by column chromatography (3% EtOAc/hex-
anes) a€orded 2.23 g (91%) of 2,2-dimethyl-6-trimethyl-
(78%) the title compound as a yellow solid. H NMR
(300 MHz, CDCl3) d: 8.27 (1H, d, J=1.9 Hz), 7.92 (1H,
d, J=7.8 Hz), 7.52 (1H, dd, J=1.9, 8.2 Hz), 7.36±7.24
(3H, m), 4.41 (2H, q, J=7.1 Hz), 2.90 (2H, s), 1.50 (6H,
s), 1.41 (3H, t, J=7.1 Hz).
Ethyl 6-[(2,2-dimethyl-4-oxo-thiochroman-6-yl)ethynyl]-
nicotinate (22). A solution of 6-ethynyl-2,2-dimethyl-
thiochroman-4-one (510.0 mg, 2.36 mmol) and ethyl 6-
iodonicotinate (654.0 mg, 2.36 mmol) in 20.0 mL Et3N
was purged with argon for 20 min. To this solution was
added Pd(PPh3)2Cl2 (425.0 mg, 0.60 mmol) and copper(I)
iodide (115.0 mg, 0.60 mmol). After sparging for an
additional 10 min with argon, the solution was stirred
overnight at room temperature. The reaction mixture
was diluted with EtOAc (20 mL) and ®ltered through a
pad of Celite using an Et2O wash. Concentration of the
®ltrate under reduced pressure, followed by column
chromatography (10 to 20% EtOAc/hexanes) of the
residual solid a€orded 675.0 mg (78%) of the title com-
1
silanylethynyl-thiochroman-4-one as an orange oil. H
NMR (300 MHz, CDCl3) d: 8.18 (1H, d, J=1.9 Hz),
7.34 (1H, dd, J=1.9, 8.1 Hz), 7.15 (1H, d, J=8.1 Hz),
2.85 (2H, s), 1.45 (6H, s), 0.23 (9H, s).
A solution of 2,2-dimethyl-6-trimethylsilanylethynyl-
thiochroman-4-one (110.0 mg, 0.38 mmol) and K2CO3
(40.0 mg, 0.29 mmol) in 10.0 mL MeOH was stirred
overnight at room temperature. The solution was dilu-
ted with H2O and extracted with Et2O. The combined
organic layers were washed with H2O and saturated
aqueous NaCl and dried over MgSO4. Removal of the
solvent under reduced pressure a€orded 81 mg (99%) of
6-ethynyl-2,2-dimethylthiochroman-4-one as an orange
oil. 1H NMR (300 MHz, CDCl3) d: 8.20 (1H, d,
J=1.9 Hz), 7.46 (1H, dd, J=1.9, 8.1 Hz), 7.18 (1H, d,
J=8.1 Hz), 3.08 (1H, s), 2.86 (2H, s), 1.46 (6H, s)
1
pound as an orange solid. H NMR (300 MHz, CDCl3)
d: 9.20 (1H, d, J=1.0 Hz), 8.34 (1H, d, J=1.8 Hz), 8.29
(1H, dd, J=2.2, 8.2 Hz), 7.60 (2H, m), 7.25 (1H, d,
J=8.4 Hz), 4.43 (2H, q, J=7.1 Hz), 2.90 (2H, s), 1.49
(6H, s), 1.43 (3H, t, J=7.1 Hz).
Ethyl 4-((2,2-dimethyl-4-tri¯uoromethanesulfonyloxy-(2H)-
thiochromen-6-yl)ethynyl)-benzoate (41). A solution of
sodium bis(trimethylsilyl)amide (1.12 g, 6.13 mmol) in
16.2 mL of THF was cooled to 78 ꢀC and a solution
of 20 (1.86 g, 5.10mmol) in 15.0 mL of THF slowly added.
After 30 min a solution of 2-[N,N-bis(tri¯uoromethane-
sulfonyl)amino]-5-pyridine (2.40 g, 6.13 mmol) in 10 mL
of THF. After 5 min the solution was warmed to room
temperature and stirred overnight. The reaction was
quenched by the addition of saturated aqueous NH4Cl
and extracted with EtOAc. The combined organic layers
were washed with 5% aqueous NaOH and H2O before
being dried (MgSO4) and concentrated under reduced
pressure. The title compound, 1.53 g (61%), was iso-
lated by column chromatography (2% EtOAc/hexanes)
A solution of 6-ethynyl-2,2-dimethylthiochroman-4-one
(82.0 mg, 0.38mmol) and ethyl 4-iodobenzoate (104.9mg,
0.38 mmol) in 5.0 mL Et3N was purged with argon for
10 min. To this solution was added Pd(PPh3)2Cl2
(88.0 mg, 0.12 mmol) and copper(I) iodide (22.9 mg,
0.12 mmol). After sparging for an additional 5 min with
argon the solution was stirred overnight at room tem-
perature. The reaction mixture was ®ltered through a
pad of Celite using an Et2O wash. Concentration of the
®ltrate under reduced pressure, followed by column
chromatography of the residual solid a€orded 100 mg
(72%) of the title compound as a yellow solid. 1H NMR
(300 MHz, CDCl3) d: 8.25 (1H, d, J=1.8 Hz), 8.00 (2H,
d, J=8.4 Hz), 7.55 (2H, d, J=8.4 Hz), 7.53 (1H, dd,
J=1.8, 8.2 Hz), 7.21 (1H, d, J=8.2 Hz), 4.37 (2H, q,
J=7.1 Hz), 2.88 (2H, s), 1.47 (6H, s), 1.39 (3H, t, J=
7.1 Hz).
1
as a yellow solid. H NMR (300 MHz, CDCl3) d: 8.03
(2H, d, J=8.4 Hz), 7.61 (1H, d, J=1.8 Hz), 7.59 (2H, d,
J=8.4 Hz), 7.41 (1H, dd, J=1.8, 8.1Hz), 7.29 (1H, d,
J=8.1 Hz), 5.91 (1H, s), 4.39 (2H, q, J=7.1 Hz), 1.53
(6H, s), 1.41 (3H, t, J=7.1 Hz).
Ethyl 4-(2,2-dimethyl-4-tri¯uoromethanesulfonyloxy-
(2H)-thiochromen-6-ylethynyl)-2-¯uorobenzoate (42). A
solution of sodium bis(trimethylsilyl)amide (0.82 g,
5.90 mmol) in 16.2 mL of THF was cooled to 78 ꢀC
and a solution of 21 (1.88 g, 4.91 mmol) in 15.0 mL
slowly added. After 30 min a solution of 2-[N,N-bis-
(tri¯uoromethanesulfonyl)amino]-5-pyridine (2.32 g,
5.90 mmol) in 10 mL of THF was added. After 5 min the
solution was warmed to room temperature and stirred
overnight. The reaction was quenched by the addition
Ethyl 4-[(2,2-dimethyl-4-oxo-thiochroman-6-yl)ethynyl]-
2-¯uorobenzoate (21). A solution of 6-ethynyl-2,2-di-
methylthiochroman-4-one (1.37 g, 6.34 mmol) and ethyl
2-¯uro-4-iodobenzoate (1.86 g, 6.34 mmol) in 40.0 mL
Et3N was purged with argon for 20 min. To this solu-
tion was added Pd(PPh3)2Cl2 (1.05 g, 1.5 mmol) and
copper(I) iodide (286.0 mg, 1.5 mmol). After sparging

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1331
of saturated aqueous NH4Cl and extracted with EtOAc.
The combined organic layers were washed with 5%
aqueous NaOH and H2O before being dried (MgSO4)
and concentrated under reduced pressure. The title
compound, 1.80 g (71%), was isolated by column chro-
in 4.0 mL of THF, tert-butyllithium (464.5mg, 7.25mmol,
4.26 mL of a 1.7 M solution in pentane), ZnCl2
(658.7 mg, 4.83 mmol) in 8.0 mL THF, 41 (1.20 g,
2.42 mmol) and Pd(PPh3)4 (111.7 mg, 0.097 mmol) in
8.0 mL THF. The title compound, 943.5 mg (87%), was
isolated by column chromatography (5% EtOAc/hex-
1
matography (5% EtOAc/hexanes) as a yellow solid. H
1
NMR (300 MHz, CDCl3) d: 7.93 (1H, d, J=7.8 Hz),
7.61 (1H, d, J=1.6 Hz), 7.43±7.27 (4H, m), 5.92 (1H, s),
4.41 (2H, q, J=7.1 Hz), 1.53 (6H, s), 1.42 (3H, t,
J=7.1 Hz).
anes) as a colorless oil. H NMR (300 MHz, CDCl3) d:
7.99 (2H, d, J=8.2 Hz), 7.52 (2H, d, J=8.4 Hz), 7.40
(5H, m), 7.35 (2H, m), 5.85 (1H, s), 4.38 (2H, q,
J=7.1 Hz), 2.72 (2H, q, J=7.6 Hz), 1.48 (6H, s), 1.40
(3H, t, J=7.1 Hz), 1.30 (3H, t, J=7.6 Hz).
Ethyl 6-(2,2-dimethyl-4-tri¯uoromethanesulfonyloxy-(2H)-
thiochromen-6-ylethynyl)-nicotinate (43). A solution of
sodium bis(trimethylsilyl)amide (284.2 mg, 1.55 mmol)
in 3.6 mL of THF was cooled to 78 ꢀC and a solution
of 22 (480.0 mg, 1.31 mmol) in 3.0 mL THF slowly
added. After 30 min a solution of 2-[N,N-bis(tri¯uoro-
methanesulfonyl)amino]-5-pyridine (608.0 mg, 1.55mmol)
in 3.0 mL of THF. After 5 min the solution was warmed
to room temperature and stirred overnight. The reac-
tion was quenched by the addition of saturated aqueous
NH4Cl and extracted with EtOAc. The combined
organic layers were washed with 5% aqueous NaOH
and H2O before being dried (MgSO4) and concentrated
under reduced pressure. The title compound was iso-
lated by column chromatography (20% EtOAc/hex-
anes) as a yellow solid, 566.0 mg (87%). 1H NMR
(300 MHz, CDCl3) d: 9.21 (1H, d, J=2.0 Hz), 8.30 (1H,
dd, J=2.0, 8.1 Hz), 7.68 (1H, d, J=1.5 Hz), 7.61 (1H, d,
J=8.2 Hz), 7.49 (1H, dd, J=1.7, 8.1 Hz), 7.31 (1H, d,
J=8.2 Hz), 5.92 (1H, s), 4.41 (2H, q, J=7.1 Hz), 1.53
(6H, s), 1.43 (3H, t, J=7.1 Hz).
Ethyl 4-[[4-(4-isopropylphenyl)-2,2-dimethyl-(2H)-thio-
chromen-6-yl]-ethynyl]-benzoate (47). Following general
procedure A and 4-isopropylbromobenzene (161.0 mg,
0.81 mmol) in 2.0 mL of THF, tert-butyllithium
(103.8 mg, 1.62 mmol, 0.95 mL of a 1.7 M solution in
pentane), ZnCl2 (175.5 mg, 1.3 mmol) in 4.0 mL THF,
41 (160.0 mg, 0.32 mmol) and Pd(PPh3)4 (24.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
128.0 mg (85%), was isolated by column chromato-
graphy (5% EtOAc/hexanes) as a colorless oil. 1H
NMR (300 MHz, CDCl3) d: 7.99 (2H, d, J=8.4 Hz),
7.53 (2H, d, J=8.1 Hz), 7.38±7.22 (7H, m), 5.86 (1H, s),
4.38 (2H, q, J=7.1 Hz), 2.98 (1H, hept, 7.0 Hz), 1.49
(6H, s), 1.43 (3H, t, J=7.1 Hz), 1.32 (6H, d, J=7.0 Hz).
Ethyl 4-[[4-(4-tert-butylphenyl)-2,2-dimethyl-(2H)-thio-
chromen-6-yl]-ethynyl]-benzoate (48). Following general
procedure A and 4-tert-butylbromobenzene (149.0 mg,
0.70mmol) in 2.0 mL of THF, tert-butyllithium (92.6 mg,
1.44 mmol, 0.85 mL of a 1.7 M solution in pentane),
ZnCl2 (133.0 mg, 0.98 mmol) in 4.0 mL THF, 41
(140.0 mg, 0.28 mmol) Pd(PPh3)4 (24.0 mg, 0.02 mmol)
in 2.0 mL THF. The title compound, 94.0 mg (70%),
was isolated by column chromatography (5% EtOAc/
hexanes) as a colorless solid. 1H NMR (300 MHz,
CDCl3) d: 7.98 (2H, d, J=8.3 Hz), 7.52 (2H, d, J=
8.3 Hz), 7.43±7.22 (7H, m), 5.86 (1H, s), 4.38 (2H, q,
J=7.1 Hz), 1.47 (6H, s), 1.40 (3H, t, J=7.1 Hz), 1.38
(9H, s).
Ethyl 4-[[4-phenyl-2,2-dimethyl-(2H)-thiochromen-6-yl]-
ethynyl]-benzoate (44). Following general procedure A,
bromobenzene (190.0 mg, 1.18 mmol), tert-butyllithium
(151.2 mg, 2.36 mmol, 1.4 mL of a 1.7 M solution in
pentane), ZnCl2 (225.0 mg, 1.4 mmol) 41 (200.0 mg,
0.40 mmol) and Pd(PPh3)4 (24.0 mg, 0.02 mmol). The
title compound, 155.0 mg (91%), was isolated by col-
umn chromatography (5% EtOAc/hexanes) as a color-
1
less solid. H NMR (300 MHz, CDCl3) d: 7.99 (2H, d,
J=8.4 Hz), 7.52 (2H, d, J=8.4 Hz), 7.42±7.24 (8H, m),
5.78 (1H, s), 4.38 (2H, q, J=7.1 Hz), 1.50 (6H, s), 1.40
(3H, t, J=7.1 Hz).
Ethyl 4-[[4-(6-methyl-pyridin-3-yl)-2,2-dimethyl-(2H)-thio-
chromen-6-yl]-ethynyl]-benzoate (49). Following general
procedure A and 5-bromo-2-methylpyridine30 (220.0 mg,
1.28 mmol) in 2.0 mL of THF, tert-butyllithium
(164.0 mg, 2.56 mmol, 1.5 mL of a 1.7 M solution in
pentane), ZnCl2 (348.0 mg, 2.56 mmol) in 4.0 mL THF,
41 (172.0 mg, 0.35 mmol) and Pd(PPh3)4 (24.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
109.0 mg (72%) was isolated by column chromato-
Ethyl 4-[[4-(4-methylphenyl)-2,2-dimethyl-(2H)-thiochro-
men-6-yl]-ethynyl]-benzoate (45). Following general pro-
cedure A and using 4-methylbromobenzene (203.0 mg,
1.15mmol) in 2.0 mL of THF, tert-butyllithium
(147.4 mg, 2.30 mmol, 1.4 mL of a 1.7 M solution in
pentane), ZnCl2 (219.4 mg, 1.4 mmol) in 4.0 mL THF,
41 (230.0 mg, 0.46 mmol) and Pd(PPh3)4 (24.0 mg,
0.02 mmol) in 2.0 mL THF, a€orded 165.0 mg (82%) of
the title compound as a colorless solid after column
chromatography (5% EtOAc/hexanes). 1H NMR
(300 MHz, CDCl3) d: 7.98 (2H, d, J=8.4 Hz), 7.51 (2H,
d, J=8.4 Hz), 7.35±7.21 (7H, m), 5.84 (1H, s), 4.38 (2H,
q, J=7.1 Hz), 2.42 (3H, s), 1.48 (6H, s), 1.40 (3H, s).
1
graphy (5% EtOAc/hexanes) as a pale-yellow solid. H
NMR (300 MHz, CDCl3) d: 8.45 (1H, d, J=2.0 Hz),
8.00 (2H, d, J=8.5 Hz), 7.52 (2H, d, J=8.5 Hz), 7.49
(1H, dd, J=2.3, 8.1 Hz), 7.36 (2H, m), 7.20 (1H, d,
J=8.1 Hz), 7.16 (1H, d, J=1.5 Hz), 5.86 (1H, s), 4.38
(2H, q, J=7.1 Hz), 2.63 (3H, s), 1.50 (6H, s), 1.40 (3H,
t, J=7.1 Hz).
Ethyl 4-[[4-(5-methyl-thiophen-2-yl)-2,2-dimethyl-(2H)-
thiochromen-6-yl]-ethynyl]-benzoate (50). Following
general procedure A and 2-methylthiophene (100.0 mg,
1.00 mmol) in 2.0 mL of THF, n-butyllithium (64.0 mg,
Ethyl 4-[[4-(4-ethylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-benzoate (46). Following general proce-
dure A and 4-ethylbromobenzene (670.9mg, 3.63mmol)

1332
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1.00 mmol, 0.63 mL of a 1.6 M solution in hexanes),
ZnCl2 (218.0 mg, 1.60 mmol) in 3.0 mL THF, 41 (200.0 mg,
0.40 mmol) and Pd(PPh3)4 (24.0mg, 0.02mmol) in 2.0 mL
THF. The title compound, 170.0 mg (96%), was isolated
by column chromatography (5% EtOAc/hexanes) as a
in 2.0 mL THF. The title compound, 158.0 mg (86%),
was isolated by column chromatography (5% EtOAc/
hexanes) as a pale-yellow solid. H NMR (300 MHz,
CDCl3) d: 7.88 (1H, d, J=7.8 Hz), 7.39±7.20 (9H,m),
5.86 (1H, s), 4.40 (2H, q, J=7.1 Hz), 2.72 (2H, q,
J=7.6 Hz), 1.49 (6H, s), 1.40 (3H, t, J=7.1 Hz), 1.30
(3H, t, J=7.6 Hz).
1
1
pale-yellow solid. H NMR (300 MHz, CDCl3) d: 8.01
(2H, d, J=8.3 Hz), 7.63 (1H, s), 7.55 (2H, d, J=8.3 Hz),
7.35 (2H, s), 6.82 (1H, d, J=3.5 Hz), 6.72 (1H, m), 6.00
(1H, s), 4.38 (2H, q, J=7.1 Hz), 2.52 (3H, s), 1.46 (6H,
s), 1.40 (2H, t, J=7.1 Hz).
Ethyl 6-[[4-(4-methylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-nicotinate (55). Following general pro-
cedure
A
and 4-methylbromobenzene (280.0 mg,
Ethyl 4-[[4-(5-ethyl-thiophen-2-yl)-2,2-dimethyl-(2H)-thio-
chromen-6-yl]-ethynyl]-benzoate (51). Following gen-
eral procedure A and 2-ethylthiophene (112.0 mg,
1.00 mmol) in 2.0 mL of THF, n-butyllithium (64.0 mg,
1.00 mmol, 0.63 mL of a 1.6 M solution in hexanes),
ZnCl2 (218.0 mg, 1.60mmol) in 3.0 mL THF, 41
(200.0 mg, 0.40mmol) and Pd(PPh3)4 (24.0 mg,
0.02mmol) in 2.0 mL THF. The title compound,
29.0 mg (16%), was isolated by HPLC (1.25% EtOAc/
1.64 mmol) in 2.0 mL of THF, tert-butyllithium
(209.5 mg, 3.27 mmol, 1.9 mL of a 1.7 M solution in
pentane), ZnCl2 (680.0 mg, 5.0 mmol) in 4.0 mL THF,
43 (120.0 mg, 0.24 mmol) and Pd(PPh3)4 (20.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
80.0 mg (76%), was isolated by column chromato-
graphy (10 to 15% EtOAc/hexanes) as a colorless solid.
1H NMR (300 MHz, CDCl3) d: 9.15 (1H, d, J=2.2 Hz),
8.23 (1H, dd, J=2.1, 8.0 Hz), 7.51 (1H, d, J=8.1 Hz),
7.40±7.32 (3H, m), 7.18 (4H, m), 5.83 (1H, s), 4.40 (2H,
q, J=7.1 Hz), 2.40 (3H, s), 1.47 (6H, s), 1.40 (3H, t,
J=7.1 Hz).
1
hexanes) as a pale-yellow solid. H NMR (300 MHz,
CDCl3) d: 8.01 (2H, d, J=8.4 Hz), 7.65 (1H, s), 7.55
(2H, d, J=8.4 Hz), 7.35 (2H, s), 6.84 (1H, d, J=3.5 Hz),
6.77 (1H, m), 6.02 (1H, s), 4.39 (2H, q, J=7.1 Hz), 2.88
(2H, q, J=7.6 Hz), 1.46 (6H, s), 1.41 (2H, t, J=7.1 Hz),
1.35 (2H, t, J=7.6 Hz).
Ethyl 6-[[4-(4-ethylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-nicotinate (56). Following general proce-
dure A and 4-ethylbromobenzene (300.0 mg, 1.62 mmol)
in 2.0 mL of THF, tert-butyllithium (207.6 mg,
3.24 mmol, 1.9 mL of a 1.7 M solution in pentane),
ZnCl2 (408.0 mg, 3.0 mmol) in 4.0 mL THF, 43
(178.0 mg, 0.36 mmol) and Pd(PPh3)4 (24 mg,
0.02 mmol) in 2.0 mL THF. The title compound was
isolated by column chromatography (10 to 15% EtOAc/
hexanes) and recrystalization from CH3CN to give
136.0 mg (83%) of pale yellow crystals. 1H NMR
(300 MHz, CDCl3) d: 9.15 (1H, s), 8.23 (1H, dd, J=2.2,
8.2 Hz), 7.51 (1H, d, J=8.1 Hz), 7.49±7.34 (3H, m),
7.24±7.17 (4H, m), 5.83 (1H, s), 4.40 (2H, q, J=7.1 Hz),
2.70 (2H, q, J=7.6 Hz), 1.47 (6H, s), 1.40 (3H, t,
J=7.1 Hz), 1.29 (3H, t, J=7.1 Hz).
Ethyl 4-[[4-(5-tert-butyl-thiophen-2-yl)-2,2-dimethyl-(2H)-
thiochromen-6-yl]-ethynyl]-benzoate (52). Following
general procedure
A
and 2-tert-butylthiophene31
(105.0 mg, 0.75 mmol) in 2.0 mL of THF, n-butyllithium
(48.1 mg, 0.75 mmol, 0.47 mL of a 1.6 M solution in
hexanes), ZnCl2 (163.2 mg, 1.20 mmol) in 3.0 mL THF,
41 (200.0 mg, 0.40 mmol) and Pd(PPh3)4 (20.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
110.0 mg (76%), was isolated by column chromato-
graphy (5% EtOAc/hexanes) as a colorless solid. 1H
NMR (300 MHz, CDCl3) d: 8.01 (2H, d, J=8.3 Hz),
7.68 (1H, s), 7.56 (2H, d, J=8.3 Hz), 7.36 (2H, m), 6.82
(2H, m), 6.04 (1H, s), 4.39 (2H, q, J=7.1 Hz), 1.46 (6H,
s), 1.43 (9H, s), 1.41 (2H, t, J=7.1 Hz).
4-[[4-Phenyl-2,2-dimethyl-(2H)-thiochromen-6-yl]-ethynyl]-
benzoic acid (57). Following general procedure B, 44
(105.0 mg, 0.247 mmol) in 3.0 mL THF and 3.0 mL
EtOH was added NaOH (120.0 mg, 3.0 mmol, 3.0 mL of
a 1 M aqueous solution). The residual solid was recrys-
tallized from CH3CN to give the title compound as a
Ethyl 4-[[4-(4-methylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-2-¯uorobenzoate (53). Following general
procedure A and 4-methylbromobenzene (280.0 mg,
1.64 mmol) in 2.0 mL of THF, tert-butyllithium
(209.5 mg, 3.27 mmol, 1.9 mL of a 1.7 M solution in
pentane), ZnCl2 (680.0 mg, 5.0 mmol) in 4.0 mL THF,
42 (200.0 mg, 0.39 mmol) and Pd(PPh3)4 (24.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
177.0 mg (79%), was isolated by column chromato-
1
pale-yellow solid. H NMR (300 MHz, acetone-d6) d:
8.00 (2H, d, J=8.4 Hz), 7.57 (2H, d, J=8.4 Hz), 7.48±
7.29 (7H, m), 7.18 (1H, d, J=1.3 Hz), 5.96 (1H, s), 1.48
(6H, s); 13C NMR (75.5 MHz, acetone-d6) d: 166.9,
141.3, 138.8, 135.9, 135.5, 133.9, 132.2, 131.5, 131.0,
130.9, 130.5, 129.9, 129.4, 128.9, 128.7, 128.3, 119.9,
92.5, 89.2, 41.7. Anal. calcd for C26H20O2S: C, 78.76; H,
5.08. Found: C, 78.44; H, 4.99.
1
graphy (5% EtOAc/hexanes) as a pale-yellow solid. H
NMR (300 MHz, CDCl3) d: 7.88 (1H, d, J=7.8 Hz),
7.28±7.18 (9H, m), 5.84 (1H, s), 4.39 (2H, q, J=7.1 Hz),
2.42 (3H, s), 1.48 (6H, s), 1.40 (3H, t, J=7.1 Hz).
Ethyl 4-[[4-(4-ethylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-2-¯uorobenzoate (54). Following general
4-[[4-(4-Methylphenyl)-2,2-dimethyl-(2H)-thiochromen-6-
yl]-ethynyl]-benzoic acid (58). Following general proce-
dure B, 45 (126.0 mg, 0.287 mmol) in 3.0 mL THF and
3.0 mL EtOH, NaOH (160.0 mg, 4.0 mmol, 2.0 mL of a
2 M aqueous solution). The residual solid was recrys-
tallized from CH3CN to give 85.0 mg (72%) the title
procedure
A and 4-ethylbromobenzene (185.0 mg,
1.00 mmol) in 2.0 mL of THF, tert-butyllithium
(128.5 mg, 2.0 mmol, 1.2 mL of a 1.7 M solution in pen-
tane), ZnCl2 (204.5 mg, 1.5 mmol) in 4.0 mL THF, 42
(200.0 mg, 0.39 mmol) and Pd(PPh3)4 (24.0 mg, 0.02 mmol)
1
compound as a pale-yellow solid. H NMR (300 MHz,

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1333
acetone-d6) d: 8.00 (2H, d, J=8.3 Hz), 7.58 (2H, d,
J=8.3 Hz), 7.45±7.38 (2H, m), 7.28±7.17 (5H, m), 5.92
(1H, s), 2.37 (3H, s), 1.47 (6H, s); 13C NMR (75.5 MHz,
acetone-d6) d: 166.9, 138.7, 138.4, 138.3, 135.9, 135.1,
134.1, 132.2, 131.4, 131.1, 130.9, 130.5, 130.0, 129.8,
128.9, 128.4, 119.8, 92.6, 89.1, 41.7, 21.1. Anal. calcd for
C27H22O2S: C, 78.99; H, 5.40. Found: C, 78.66; H, 5.21.
8.3 Hz), 7.56 (1H, dd, J=2.1 8.0 Hz), 7.45 (2H, m), 7.31
(1H, d, J=8.0 Hz), 7.06 (1H, s), 6.06 (1H, s), 2.51 (3H,
s), 1.44 (6H, s); 13C NMR (75.5 MHz, DMSO-d6) d:
166.6, 157.5, 148.5, 136.6, 135.6, 134.4, 133.9, 132.4,
132.1, 131.5, 130.9, 130.5, 129.4, 129.3, 128.3, 126.4,
122.8, 118.5, 91.5, 88.6, 41.0, 28.4, 23.8. Anal. calcd for
C26H21NO2S: C, 75.89; H, 5.14. Found: C, 75.68; H,
4.92.
4-[[4-(4-Ethylphenyl)-2,2-dimethyl-(2H)-thiochromen-6-yl]-
ethynyl]-benzoic acid (59). Following general procedure
B and 46 (940.0 mg, 2.08 mmol) in 10.0 mL THF and
5.0 mL EtOH, and NaOH (416.0 mg, 10.4 mmol, 5.2 mL
of a 2 M aqueous solution). The residual solid was
recrystallized from CH3CN to give 786.0 mg (89%) of
the title compound as a colorless solid. 1H NMR
(300 MHz, acetone-d6) d: 8.01 (2H, d, J=8.3 Hz), 7.60
(2H, d, J=8.5 Hz), 7.42 (2H, m), 7.29 (2H, m), 7.22
(3H, m), 5.94 (1H, s), 2.69 (2H, q, J=7.7 Hz), 1.47 (6H,
s), 1.25 (3H, t, J=7.7 Hz); 13C NMR (75.5 MHz, ace-
tone-d6) d: 166.9, 144.8, 138.7, 138.6, 135.9, 135.1,
134.1, 132.2, 131.4, 131.0, 130.9, 130.5, 129.9, 128.9,
128.8, 128.4, 119.8, 92.6, 89.1, 41.7, 30.1, 29.0, 15.9.
4-[[4-(5-Methyl-thiopen-2-yl)-2,2-dimethyl-(2H)-thiochro-
men-6-yl]-ethynyl]-benzoic acid (63). Following general
procedure B and 50 (143.0 mg, 0.322 mmol) in 3.0 mL
THF and 3.0 mL EtOH, and NaOH (160.0 mg,
4.0 mmol, 4.0 mL of a 1 M aqueous solution). The resi-
dual solid was recrystallized from CH3CN to give
110.0 mg (82%) of the title compound as a pale-yellow
1
solid. H NMR (300 MHz, acetone-d6) d: 8.03 (2H, d,
J=8.4 Hz), 7.63 (2H, d, J=8.3 Hz), 7.60 (1H, s), 7.44
(2H, s), 6.87 (1H, d, J=3.5 Hz), 6.79 (1H, m), 6.10 (1H,
s), 2.49 (3H, s), 1.45 (6H, s); 13C NMR (75.5 MHz, ace-
tone-d6) d: 166.9, 140.7, 140.3, 135.9, 135.4, 133.4,
132.3, 132.2, 131.7, 131.1, 131.0, 130.5, 129.0, 128.4,
127.8, 126.5, 120.0, 92.5, 89.3, 41.7, 28.7, 15.2. Anal.
calcd for C25H20O2S2: C, 72.08; H, 4.84. Found: C,
71.80; H, 4.84.
4-[[4-(4-Isopropylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-benzoic acid (60). Following general pro-
cedure B and 47 (89.0 mg, 0.19 mmol) in 3.0 mL THF
and 3.0 mL EtOH, and NaOH (80.0 mg, 2.0 mmol,
2.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 78.0 mg (93%)
4-[[4-(5-Ethyl-thiophen-2-yl)-2,2-dimethyl-(2H)-thiochro-
men-6-yl]-ethynyl]-benzoic acid (64). Following general
procedure B and 51 (23.0 mg, 0.05 mmol) in 1.0 mL
THF and 1.0 mL EtOH, and NaOH (40.0 mg, 1.0 mmol,
1.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 15.5 mg (72%)
of the title compound as an orange solid. 1H NMR
(300 MHz, acetone-d6) d: 8.03 (2H, d, J=8.3 Hz), 7.63
(2H, d, J=8.3 Hz), 7.61 (1H, s), 7.44 (2H, s), 6.90 (1H,
d, J=3.5 Hz), 6.83 (1H, d, J=3.5 Hz), 6.10 (1H, s), 2.86
(2H, q, J=7.6 Hz), 1.45 (6H, s), 1.30 (3H, t, J=7.6 Hz);
13C NMR (75.5 MHz, acetone-d6) d: 166.9, 148.3, 140.0,
136.0, 135.5, 133.4, 132.3, 132.2, 131.7, 131.1, 130.0,
130.6, 129.1, 128.4, 127.6, 124.8, 120.0, 92.6, 89.3, 41.7,
28.7, 23.9, 16.2.
1
of the title compound as a pale-yellow solid. H NMR
(300 MHz, acetone-d6) d: 8.00 (2H, d, J=8.4 Hz), 7.58
(2H, d, J=8.4 Hz), 7.45±7.21 (7H, m), 5.93 (1H, s), 2.95
(1H, hept, J=7.0 Hz), 1.47 (6H, s), 1.25 (6H, d,
J=7.0 Hz); 13C NMR (75.5 MHz, acetone-d6) d: 166.9,
149.4, 138.7, 135.9, 135.2, 134.0, 132.2, 131.5, 131.0,
130.9, 130.5, 129.8, 128.9, 128.4, 127.3, 119.8, 92.6, 89.1,
41.7, 34.5, 24.2. Anal. calcd for C29H26O2S: C, 79.42; H,
5.98. Found: C, 79.15; H, 5.80.
4-[[4-(4-tert-Butylphenyl)-2,2-dimethyl-(2H)-thiochromen-
6-yl]-ethynyl]-benzoic acid (61). Following general pro-
cedure B and 48 (65.0 mg, 0.135 mmol) in 2.0 mL THF
and 2.0 mL EtOH, and NaOH (80.0 mg, 2.0 mmol,
2.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 33.0 mg (54%)
4-[[4-(5-tert-Butylthiopen-2-yl)-2,2-dimethyl-(2H)-thiochro-
men-6-yl]-ethynyl]-benzoic acid (65). Following general
procedure B and 52 (88.0 mg, 0.181 mmol) in 2.0 mL
THF and 2.0 mL EtOH, and NaOH (160.0 mg,
4.0 mmol, 4.0 mL of a 1 M aqueous solution). The resi-
dual solid was recrystallized from CH3CN to give
68.0 mg (82%) of the title compound as a pale-yellow
1
of the title compound as a pale-yellow solid. H NMR
(300 MHz, acetone-d6) d: 8.01 (2H, d, J=8.4 Hz), 7.57
(2H, d, J=8.4 Hz), 7.45 (4H, m), 7.24 (3H, m), 5.93
(1H, s), 1.47 (6H, s), 1.34 (9H, s); 13C NMR (75.5 MHz,
acetone-d6) d: 166.9, 151.6, 138.6, 138.3, 135.9, 135.3,
134.0, 132.2, 131.5, 131.0, 130.5, 129.6, 129.0, 128.4,
126.2, 119.8, 92.6, 89.2, 41.7, 35.1, 31.6. Anal. calcd for
C30H28O2S: C, 79.61; H, 6.24. Found: C, 79.25; H, 5.92.
1
solid. H NMR (300 MHz, acetone-d6) d: 8.03 (2H, d,
J=8.3 Hz), 7.63 (2H, d, J=8.3 Hz), 7.62 (1H, s), 7.44
(2H, d, J=1.2 Hz), 6.87 (2H, s), 6.11 (1H, s), 1.45 (6H,
s), 1.39 (9H, s). 13C NMR (75.5 MHz, acetone-d6) d:
166.9, 157.9, 139.5, 136.0, 135.4, 133.3, 132.3, 132.2,
131.7, 131.1, 131.0, 130.6, 129.1, 128.4, 127.3, 122.8,
120.0, 92.6, 89.3, 41.7, 35.2, 32.7, 32.6, 28.7. Anal. calcd
for C28H26O2S2: C, 73.32; H, 5.71. Found: C, 72.97; H,
5.62.
4-[[4-(6-Methylpyridin-3-yl)-2,2-dimethyl-(2H)-thiochro-
men-6-yl]-ethynyl]-benzoic acid (62). Following general
procedure B and 49 (70.0 mg, 0.159 mmol) in 3.0 mL
THF and 3.0 mL EtOH, and NaOH (120.0 mg,
3.0 mmol, 3.0 mL of a 1 M aqueous solution). The resi-
dual solid was recrystallized from acetone to give
60.0 mg (92%) of the title compound as a colorless
4-[[4-(4-Methylphenyl)-2,2-dimethyl-(2H)-thiochromen-6-
yl]-ethynyl]-2-¯uorobenzoic acid (66). Following general
procedure B and 53 (100.0 mg, 0.219 mmol) in 3.0 mL
THF and 3.0 mL EtOH, and NaOH (80.0 mg, 2.0 mmol,
1
solid. H NMR (300 MHz, acetone-d6) d: 8.36 (1H, d,
J=2.1 Hz), 7.91 (2H, d, J=8.3 Hz), 7.60 (2H, d, J=

1334
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
2.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 78.0 mg (83%)
of the title compound as a pale-yellow solid. H NMR
temperature. After stirring for 21 h the mixture was
poured into 200 mL H2O. The organic layer was washed
with 5% aqueous NaOH, H2O, and dried over MgSO4.
Removal of the solvent under reduced pressure and
distillation of the residue a€orded 20.6 g (83%) of the
product as a colorless oil, bp 93±95 ꢀC/2 mm.
1
(300 MHz, acetone-d6) d: 7.94 (1H, d, J=7.8 Hz), 7.43±
7.17 (9H, m), 5.93 (1H, s), 2.38 (3H, s), 1.47 (6H, s); 13C
NMR (75.5 MHz, acetone-d6) d: 164.6 (d, J=1.5 Hz),
162.4 (d, J=259.1 Hz), 138.6, 138.3 (d, J=8.8 Hz),
136.3, 135.1, 134.1, 133.4, 133.3, 131.5, 131.1, 130.1 (d,
J=10.4 Hz), 130.0, 129.8, 129.0, 128.0 (d, J=3.7 Hz),
120.2 (d, J=24.4 Hz), 119.6 (d, J=10.7 Hz), 119.4, 93.5,
87.9 (d, J=2.8 Hz), 41.8, 21.2. Anal. calcd for C27H21
FO2S: C, 75.68; H, 4.94. Found: C, 75.77; H, 4.87.
2-Hydroxy-5-bromo-acetophenone (25). A mixture of
AlCl3 (6.20 g, 46.50 mmol) 24 (10.0 g, 46.50 mmol) was
heated to 150 ꢀC for 30 min while a stream of argon was
passed over the molten solid. Upon cooling to room
temperature the orange solid was carefully treated with
100 mL of H2O and 100 mL of 10% aqueous HCl. The
resulting mixture was extracted with EtOAc and the
combined organic layers washed with H2O and satu-
rated aqueous NaCl before being dried over Na2SO4.
Concentration of the solution under reduced pressure
a€orded a tan solid which after recrystallization from i-
PrOH provided 7.18 g (72%) of the title compound as
an o€-white crystalline solid. 1H NMR (300 MHz,
CDCl3) d: 12.17 (1H, s), 7.84 (1H, d, J=2.6 Hz), 7.55
(1H, dd, J=2.5, 9.0 Hz), 6.90 (1H, d, J=8.9 Hz), 2.64
(3H, s).
4-[[4-(4-Ethylphenyl)-2,2-dimethyl-(2H)-thiochromen-6-yl]-
ethynyl]-2-¯uorobenzoic acid (67). Following general
procedure B and 54 (125.0 mg, 0.266 mmol) in 3.0 mL
THF and 3.0 mL EtOH, and NaOH (120.0 mg,
3.0 mmol, 3.0 mL of a 1 M aqueous solution). The resi-
dual solid was recrystallized from CH3CN to give
100.0 mg (86%) of the title compound as a pale-yellow
1
solid. H NMR (300 MHz, acetone-d6) d: 7.94 (1H, d
J=7.8 Hz), 7.43±7.20 (9H, m), 5.93 (1H, s), 2.68 (2H, q,
J=7.6 Hz), 1.47 (6H, s), 1.24 (3H, t, J=7.6 Hz); 13C
NMR (75.5 MHz, acetone-d6) d: 164.6 (d, J=3.2 Hz),
162.4 (d, J=259.3 Hz), 144.8, 138.6 (d, J=11.0 Hz),
136.4, 135.2, 134.1, 133.3, 131.5, 131.1, 130.1 (d, J=
10.7 Hz), 129.8, 129.0, 128.8, 128.0 (d, J=3.5 Hz), 120.2
(d, J=24.4 Hz), 119.5 (d, J=10.1 Hz), 119.4, 93.5, 87.9
(d, J=3.1 Hz), 41.8, 41.6, 30.6, 15.9.
2,2-Dimethyl-6-bromo-chroman-4-one (26). To a solu-
tion of piperidine (2.83 g, 33.25 mmol) in 45 mL benzene
was added tri¯uoroacetic acid (344.6 mg, 3.02 mmol) as
a solution in 4.0 mL of benzene. Acetone (8.78 g,
151.3 mmol) was added followed by 25 (6.50 g,
30.23 mmol). The resulting solution was heated to re¯ux
in a ¯ask ®tted with a Dean±Stark trap. After 24 h, an
additional 2.5 equiv of acetone and 0.1 equiv of tri-
¯uoroacetic acid were added. After a total of 43 h the
reaction was cooled to room temperature and diluted
with EtOAc. The solution was washed with 1 M aqu-
eous HCl, H2O, and saturated aqueous NaCl before
being dried (MgSO4) and concentrated under reduced
pressure. Distillation of the residual oil (bulb-to-bulb)
a€orded 4.80 g (62%) of the title compound as a clear
6-[[4-(4-Methylphenyl)-2,2-dimethyl-(2H)-thiochromen-6-
yl]-ethynyl]-nicotinic acid (68). Following general proce-
dure B and 55 (66.0 mg, 0.15 mmol) in 2.0 mL THF and
2.0 mL EtOH, and NaOH (80.0 mg, 2.0 mmol, 2.0 mL of
a 1 M aqueous solution). The solvent was removed
under reduced pressure to give the title compound as a
1
yellow solid, 50.0 mg (81%). H NMR (300 MHz, ace-
tone-d6) d: 9.09 (1H, d, J=1.4 Hz), 8.30 (1H, dd, J=2.0,
8.1 Hz), 7.65 (1H, d, J=8.1 Hz), 7.46 (2H, s), 7.24 (5H,
m), 5.94 (1H, s), 2.37 (3H, s), 1.48 (6H, s); 13C NMR
(75.5 MHz, acetone-d6) d: 166.0, 151.8, 147.5, 138.6,
138.4, 138.2, 138.1, 136.8, 135.1, 134.1, 131.6, 131.5,
130.0, 129.8, 129.0, 127.5, 125.9, 118.9, 91.7, 89.3, 21.1.
yellow oil, bp 105±115 ꢀC/5 mm. H NMR (300 MHz,
1
CDCl3) d: 7.97 (1H, d, J=2.6 Hz), 7.54 (1H, dd, J=2.6,
8.7 Hz), 6.84 (1H, d, J=8.8 Hz), 2.72 (2H, s), 1.46 (6H,
s).
6-[[4-(4-Ethylphenyl)-2,2-dimethyl-(2H)-thiochromen-6-yl]-
ethynyl]-nicotinic acid (69). Following general procedure
B and 56 (110.0 mg, 0.24 mmol) in 3.0 mL THF and
3.0 mL EtOH, and NaOH (120.0 mg, 3.0 mmol, 3.0 mL
of a 1 M aqueous solution). The solvent was removed
under reduced pressure to give 100 mg (96%) of the title
compound as a colorless solid. 1H NMR (300 MHz,
acetone-d6) d: 9.08 (1H, d, J=2.0 Hz), 8.30 (1H, dd,
J=2.2, 8.2 Hz), 7.66 (1H, d, J=8.2 Hz), 7.46 (2H, s),
7.31±7.21 (5H, m), 5.95 (1H, s), 2.69 (2H, q, J=7.6 Hz),
1.48 (6H, s), 1.25 (3H, t, J=7.6Hz); 13C NMR (75.5 MHz,
acetone-d6) d: 165.9, 151.8, 147.5, 144.8, 138.6, 138.5,
138.1, 136.8, 135.2, 134.1, 131.7, 131.5, 129.9, 129.0,
128.8, 127.6, 125.8, 118.9, 91.8, 89.3, 41.8, 29.1, 15.9.
2,2-Dimethyl-6-trimethylsilanylethynyl-chroman-4-one
(27). A solution of 26 (4.30 g, 16.85 mmol) and copper
(I) iodide (321 mg, 0.17 mmol) in 55.0 mL Et3N was
sparged with argon for 30 min. To this solution was
added trimethylsilylacetylene (4.66 g, 50.56 mmol) and
bis(triphenylphosphine)palladium(II) chloride (1.18 g,
0.17 mmol). The mixture was heated to 70 ꢀC for 26 h,
cooled to room temperature, and diluted with Et2O
(100 mL). The resulting mixture was ®ltered through a
pad of Celite using an Et2O wash and the ®ltrate washed
with H2O, a solution of NH4OH saturated aqueous
NH4Cl (9/1), H2O, 1 M aqueous HCl, H2O and satu-
rated aqueous NaCl before being dried (Na2SO4) and
concentrated under reduced pressure. Column chroma-
tography (5% EtOAc/hexanes) of the residual oil a€or-
ded 4.09 g (89%) of the product as a yellow waxy solid.
1H NMR (300 MHz, CDCl3) d: 7.99 (1H, d, J=2.1 Hz),
7.53 (1H, dd, J=2.2, 8.6 Hz), 6.86 (1H, d, J=8.6 Hz),
2.72 (2H, s), 1.45 (6H, s), 0.24 (9H, s).
4-Bromophenylacetate (24). To a solution of 4-bromo-
phenol (20.0 g, 0.121 mol) in 200 mL CH2Cl2 was added
triethylamine (14.0 g, 0.139 mol) followed by acetyl
chloride (9.53 g, 0.121 mol) in small portions at room

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1335
Ethyl 4-[(2,2-dimethyl-4-oxo-chroman-6-yl)ethynyl]-
benzoate (28). To a solution of 27 (4.05 g, 14.87 mmol)
in 60.0 mL of MeOH was added K2CO3 (410.9 mg,
2.97 mmol) The resulting mixture stirred at room tem-
perature for 24 h, diluted with EtOAc (100 mL) and
washed with H2O and saturated aqueous NaCl, and
dried over Na2SO4. Concentration of this solution
under reduced pressure a€orded 2.71 g (91%) of 2,2-
dimethyl-6-ethynyl-chroman-4-one as a tan solid. 1H
NMR (300 MHz, CDCl3) d: 8.01 (1H, d, J=2.2 Hz),
7.56 (1H, dd, J=2.2, 8.6 Hz), 6.90 (1H, d, J=8.6 Hz),
3.02 (1H, s), 2.74 (2H, s), 1.47 (6H, s).
pressure. The title compound, 2.0 g (64%), was isolated
by column chromatography (5% EtOAc/hexanes) as a
colorless solid. 1H NMR (300 MHz, CDCl3) d: 8.03 (2H,
d, J=8.3 Hz), 7.57 (2H, d, J=8.3 Hz), 7.45±7.21 (2H, m),
6.85 (1H, d, J=8.4 Hz), 5.69 (1H, s), 4.40 (2H, q,
J=7.1 Hz), 1.55 (6H, s), 1.4 (3H, t, J=7.1 Hz).
Ethyl 2-¯uoro-4-((2,2-dimethyl-4-tri¯uoromethanesulf-
onyloxy-(2H)-chromen-6-yl)ethynyl)-benzoate (71).
A
solution of sodium bis(trimethylsilyl)amide (238.0 mg,
1.30 mmol) in 3.0 mL of THF was cooled to 78 ꢀC and
a solution of ethyl 4-((2,2-dimethyl-4-oxo-chroman-6-
yl)ethynyl)-benzoate (400.0 mg, 1.09 mmol) in 2.0 mL
slowly added. After 30 min a solution of 2-[N,N-bis(tri-
A solution of the alkyne (2.60 g, 13.0 mmol) and ethyl 4-
iodobenzoate (3.6 g, 13.0 mmol) in 50.0 mL Et3N was
purged with argon for 15 min. To this solution was
added Pd(PPh3)2Cl2 (1.82 g, 2.6 mmol) and copper(I)
iodide (496 mg, 2.6 mmol). After sparging for an addi-
tional 10 min with argon, the solution was stirred over-
night at room temperature. The reaction mixture was
®ltered through a pad of Celite using an Et2O wash.
Concentration of the ®ltrate under reduced pressure
followed by column chromatography (2±5% EtOAc/
hexanes) of the residual solid a€orded 2.28 g (50%) the
title compound as an orange solid. 1H NMR (300 MHz,
CDCl3) d: 8.06 (1H, d, J=2.2 Hz), 8.02 (2H, d, J=
8.5 Hz), 2.61 (1H, dd, J=2.2, 8.6 Hz), 7.55 (2H, d, J=
8.5 Hz), 6.93 (1H, d, J=8.6 Hz), 4.39 (2H, q, J=7.1 Hz),
2.75 (3H, s), 1.48 (6H, s), 1.41 (t, J=7.1 Hz).
¯uoromethanesulfonyl)-amino]-5-pyridine
(510.0 mg,
1.30 mmol) in 1.0 mL of THF was added. After 5 min
the solution was warmed to room temperature and stir-
red overnight. The reaction was quenched by the addi-
tion of saturated aqueous NH4Cl and extracted with
EtOAc. The combined organic layers were washed with
5% aqueous NaOH and H2O before being dried
(MgSO4) and concentrated under reduced pressure. The
title compound, 315.0 mg (58%), was isolated by col-
umn chromatography (5% EtOAc/hexanes) as a color-
1
less solid. H NMR (300 MHz, CDCl3) d: 7.92 (1H, d,
J=7.8 Hz), 7.44±7.26 (4H, m), 6.85 (1H, d, J=8.7 Hz),
5.70 (1H, s), 4.31 (2H, q, J=7.1 Hz), 1.55 (6H, s), 1.41
(3H, t, J=7.1 Hz).
Ethyl 4-[[4-phenyl-2,2-dimethyl-(2H)-chromen-6-yl]-eth-
ynyl]-benzoate (72). Following general procedure A and
bromobenzene (250.0 mg, 1.59 mmol) in 3.0 mL of THF,
tert-butyllithium (203.7 mg, 3.18 mmol, 1.9 mL of a
1.7 M solution in pentane), ZnCl2 (440.0 mg, 3.18 mmol)
in 5.0 mL THF, 70 (150.0 mg, 0.31 mmol) and Pd
(PPh3)4 (24.0 mg, 0.02 mmol) in 2.0 mL THF. The title
compound, 110.0 mg (87%), was isolated by column
chromatography (2.5% EtOAc/hexanes) as a colorless
solid. 1H NMR (300 MHz, CDCl3) d: 7.99 (2H, d,
J=8.3 Hz), 7.51 (2H, d, J=8.3 Hz), 7.47±7.35 (6H, m),
7.21 (1H, d, J=2.0 Hz), 6.88 (1H, d, J=8.4 Hz), 5.66
(1H, s), 4.38 (2H, q, J=7.1 Hz), 1.52 (6H, s), 1.40 (3H,
t, J=7.1 Hz).
Ethyl 2-¯uoro-4-[(2,2-dimethyl-4-oxo-chroman-6-yl)-
ethynyl]-benzoate (29). A solution of 6-ethynyl-2,2-
dimethylchroman-4-one (314.0 mg, 1.57mmol) and ethyl
2-¯uoro-4-iodobenzoate (440.0 mg, 1.50 mmol) in
10.0 mL Et3N was purged with argon for 15 min. To this
solution was added Pd(PPh3)2Cl2 (275.0 mg, 0.39 mmol)
and copper(I) iodide (75.0 mg, 0.39 mmol). After spar-
ging for an additional 10 min with argon, the solution
was stirred overnight at room temperature. The reaction
mixture was ®ltered through a pad of Celite using an
Et2O wash. Concentration of the ®ltrate under reduced
pressure, followed by column chromatography (3±5%
EtOAc/hexanes) of the residual solid a€orded 400.0 mg
1
(69%) the title compound as an orange solid. H NMR
(300 MHz, CDCl3) d: 8.05 (1H, d, J=2.1 Hz), 7.90 (1H,
d, J=7.8 Hz), 7.60 (1H, dd, J=2.2 8.5 Hz), 7.29 (1H,
dd, J=1.5, 8.2 Hz), 7.25 (1H, d, J=11.4 Hz), 6.93 (1H,
d, J=8.5 Hz), 4.39 (2H, q, J=7.1 Hz), 2.75 (2H, s), 1.48
(6H, s), 1.40 (3H, t, J=7.1 Hz).
Ethyl 4-[[4-(4-methylphenyl)-2,2-dimethyl-(2H)-chromen-
6-yl]-ethynyl]-benzoate (73). Following general proce-
dure A and 4-methylbromobenzene (237.0 mg, 1.38mmol)
in 3.0 mL of THF, tert-butyllithium (177.5 mg,
2.77 mmol, 1.6 mL of a 1.7 M solution in pentane),
ZnCl2 (377.0 mg, 2.77 mmol) in 5.0 mL THF, 70
(150.0 mg, 0.31mmol) and Pd(PPh3)4 (24.0 mg,
0.02mmol) in 2.0 mL THF. The title compound,
120.0 mg (92%), was isolated by column chromato-
Ethyl 4-(2,2-dimethyl-4-tri¯uoromethanesulfonyloxy-(2H)-
chromen-6-ylethynyl)-benzoate (70).
A
solution of
sodium bis(trimethylsilyl)amide (1.56 g, 8.5 mmol) in
18.0 mL of THF was cooled to 78 ꢀC and a solution of
28 (2.26 g, 6.49 mmol) in 15.0 mL slowly added. After
1
graphy (2.5% EtOAc/hexanes) as a colorless solid. H
NMR (300 MHz, CDCl3) d: 7.98 (2H, d, J=8.5 Hz),
7.50 (2H, d, J=8.5 Hz), 7.34 (1H, dd, J=2.1, 8.3 Hz),
7.25±7.21 (5H, m), 6.85 (1H, d, J=8.3 Hz), 5.62 (1H, s),
4.36 (2H, q, J=7.1 Hz), 2.41 (3H, s), 1.49 (6H, s), 1.39
(3H, t, J=7.1 Hz).
30 min
a
solution of 2-[N,N-bis(tri¯uoromethane-
sulfonyl)amino]-5-pyridine (3.10 g, 7.79 mmol) in 10 mL
of THF. After 5 min the solution was warmed to room
temperature and stirred overnight. The reaction was
quenched by the addition of saturated aqueous NH4Cl
and extracted with EtOAc. The combined organic layers
were washed with 5% aqueous NaOH and H2O before
being dried (MgSO4) and concentrated under reduced
Ethyl 4-[[4-(4-ethylphenyl)-2,2-dimethyl-(2H)-chromen-6-
yl]-ethynyl]-benzoate (74). Following general procedure
A and 4-ethylbromobenzene (280.0 mg, 1.51 mmol) in

1336
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
3.0 mL of THF, tert-butyllithium (198.6 mg, 3.10 mmol,
1.9 mL of a 1.7 M solution in pentane), ZnCl2 (408.0 mg,
3.10 mmol) in 5.0 mL THF, 70 (150.0 mg, 0.31 mmol)
and Pd(PPh3)4 (24.0 mg, 0.02 mmol) in 2.0 mL THF.
The title compound, 123.0 mg (91%), was isolated by
column chromatography (2.5% EtOAc/hexanes) as a
procedure A and 4-ethylbromobenzene (150.0 mg,
0.80mmol) in 3.0 mL of THF, tert-butyllithium
(102.5mg, 1.60 mmol, 0.94 mL of a 1.7 M solution in
pentane), ZnCl2 (218.0 mg, 1.60 mmol) in 5.0 mL THF,
71 (160.0 mg, 0.32 mmol) and Pd(PPh3)4) (20.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
115.0 mg (79%), was isolated by column chromato-
graphy (5% EtOAc/hexanes) as a colorless solid. 1H
NMR (300 MHz, CDCl3) d: 7.88 (1H, d, J=7.8 Hz),
7.35 (1H, dd, J=2.0, 8.3 Hz), 7.28±7.20 (7H, m), 6.88
(1H, d, J=8.3 Hz), 5.65 (1H, s), 4.39 (2H, q, J=7.1 Hz),
2.73 (2H, q, J=7.6 Hz), 1.52 (6H, s), 1.40 (3H, t,
J=7.1 Hz), 1.31 (3H, t, J=7.6 Hz).
1
pale-yellow solid. H NMR (300 MHz, CDCl3) d: 8.00
(2H, d, J=8.4 Hz), 7.52 (2H, d, J=8.4 Hz), 7.36 (1H,
dd, J=2.0, 8.3 Hz), 7.31±7.25 (5H, m), 6.88 (1H, d,
J=8.3 Hz), 5.65 (1H, s), 4.38 (2H, q, J=7.1 Hz), 2.73
(2H, q, J=7.6 Hz), 1.52 (6H, s), 1.41 (3H, t, J=7.1 Hz),
1.31 (2H, t, J=7.6 Hz).
Ethyl 4-[[4-(4-(1-methylethyl)phenyl)-2,2-dimethyl-(2H)-
chromen-6-yl]-ethynyl]-benzoate (75). Following general
procedure A and 4-iso-propylbromobenzene (250.0 mg,
1.25 mmol) in 3.0 mL of THF, tert-butyllithium
(160.8 mg, 2.51 mmol, 1.5 mL of a 1.7 M solution in
pentane), ZnCl2 (345.0 mg, 2.53 mmol) in 5.0 mL THF,
70 (150.0 mg, 0.31 mmol) and Pd(PPh3)4 (24.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
100.0 mg (72%), was isolated by column chromato-
4-[[4-Phenyl-2,2-dimethyl-(2H)-chromen-6-yl]-ethynyl]-
benzoic acid (79). Following general procedure B and
72 (70.0 mg, 0.171 mmol) in 3.0 mL THF and 3.0 mL
EtOH, and NaOH (120.0 mg, 3.0 mmol, 3.0 mL of a 1 M
aqueous solution). The residual solid was recrystallized
from CH3CN to give 48.0 mg (74%) the title compound
as a colorless solid. 1H NMR (300 MHz, acetone-d6)
d: 8.00 (2H, d, J=8.2 Hz), 7.57 (2H, d, J=8.2 Hz), 7.51±
7.37 (6H, d), 7.14 (1H, d, J=2.0 Hz), 6.91 (1H, d,
J=8.3 Hz), 5.80 (1H, s), 1.50 (6H, s); 13C NMR
(75.5 MHz, acetone-d6) d: 167.0, 155.2, 138.6, 134.6,
133.8, 132.1, 131.0, 130.7, 130.5, 129.5, 129.4, 129.3,
128.9, 128.7, 123.4, 118.2, 115.4, 93.0, 87.9, 77.4, 27.8.
Anal. calcd for C26H20O3: C, 82.08; H, 5.30. Found: C,
81.85; H, 5.02.
1
graphy (2.5% EtOAc/hexanes) as a colorless solid. H
NMR (300 MHz, CDCl3) d: 7.99 (2H, d, J=8.3 Hz),
7.52 (2H, d, J=8.3 Hz), 7.36 (1H, dd, J=2.1, 8.3 Hz),
7.30±7.26 (5H, m), 6.88 (1H, d, J=8.3 Hz), 5.64 (1H, s),
4.38 (2H, q, J=7.1 Hz), 2.98 (1H, hept, J=7.0 Hz), 1.51
(6H, s), 1.40 (3H, t, J=7.1 Hz), 1.31 (6H, d, J=7.0 Hz).
Ethyl 4-[[4-(4-(1,1-dimethylethyl)phenyl)-2,2-dimethyl-
(2H)-chromen-6-yl]-ethynyl]-benzoate (76). Following
general procedure A and 4-tert-butylbromobenzene
(280.0 mg, 1.61 mmol) in 3.0 mL of THF, tert-butyl-
lithium (206.3 mg, 3.22 mmol, 1.7 mL of a 1.7 M solu-
tion in pentane), ZnCl2 (380.0 mg, 3.22 mmol) in 5.0 mL
THF, 70 (150.0 mg, 0.31 mmol) Pd(PPh3)4 (24.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
85.0 mg (59%), was isolated by column chromato-
4-[[4-(4-Methylphenyl)-2,2-dimethyl-(2H)-chromen-6-yl]-
ethynyl]-benzoic acid (80). Following general procedure
B and 73 (90.0 mg, 0.213 mmol) in 3.0 mL THF and
3.0 mL EtOH, and NaOH (120.0 mg, 3.0 mmol, 3.0 mL
of a 1 M aqueous solution). The residual solid was
recrystallized from CH3CN to give 70.0 mg (83%) the
title compound as a colorless solid. 1H NMR (300 MHz,
acetone-d6) d: 8.01 (2H, d, J=8.3 Hz), 7.57 (2H, d,
J=8.3 Hz), 7.40 (1H, dd, J=2.1, 8.3 Hz), 7.30±7.20 (4H,
m), 7.16 (1H, d, J=2.0 Hz), 6.90 (1H, d, J=8.3 Hz),
5.67 (1H, s), 2.38 (3H, s), 1.49 (6H, s); 13C NMR
(75.5 MHz, acetone-d6) d: 166.9, 155.2, 138.6, 135.7,
134.5, 133.7, 132.1, 130.6, 130.5, 130.1, 129.3, 128.8,
123.5, 118.2, 115.3, 93.1, 87.9, 77.4, 27.9, 21.2.
1
graphy (2.5% EtOAc/hexanes) as a colorless solid. H
NMR (300 MHz, CDCl3) d: 7.99 (2H, d, J=8.3 Hz),
7.53 (2H, d, J=8.3 Hz), 7.45 (1H, d, J=8.4 Hz), 7.37
(1H, dd, J=2.0, 8.3 Hz), 7.32±7.28 (3H, m), 6.89 (1H, d,
J=8.3 Hz), 5.66 (1H, s), 4.39 (2H, q, J=7.1 Hz), 1.52
(6H, s), 1.40 (3H, t, J=7.1 Hz), 1.39 (9H, s).
Ethyl 2-¯uoro-4-[[4-(4-methylphenyl)-2,2-dimethyl-(2H)-
chromen-6-yl]-ethynyl]-benzoate (77). Following general
procedure A and 4-methylbromobenzene (140.0 mg,
0.80 mmol) in 3.0 mL of THF, tert-butyllithium
(102.5 mg, 1.60 mmol, 0.94 mL of a 1.7 M solution in
pentane), ZnCl2 (174.0 mg, 1.28 mmol) in 5.0 mL THF,
71 (150.0 mg, 0.31 mmol) and Pd(PPh3)4 (20.0 mg,
0.02 mmol) in 2.0 mL THF. The title compound,
86.0 mg (62%), was isolated by column chromato-
graphy (5% EtOAc/hexanes) as a colorless solid. 1H
NMR (300 MHz, CDCl3) d: 7.88 (1H, d, J=7.8 Hz),
7.35 (1H, d, J=7.8 Hz), 7.35 (1H, dd, J=2.0, 8.4 Hz),
7.28±7.19 (7H, m), 6.88 (1H, d, J=8.3 Hz), 5.64 (1H, s),
4.40 (2H, q, J=7.1 Hz), 2.43 (3H, s), 1.51 (6H, s), 1.41
(3H, t, J=7.1 Hz).
4-[[4-(4-Ethylphenyl)-2,2-dimethyl-(2H)-chromen-6-yl]-
ethynyl]-benzoic acid (81). Following general procedure
B and 74 (82.0 mg, 0.188 mmol) in 3.0 mL THF and
3.0 mL EtOH, and NaOH (120.0 mg, 3.0 mmol, 3.0 mL
of a 1 M aqueous solution). The residual solid was
recrystallized from CH3CN to give 65.0 mg (85%) the
title compound as a colorless solid. 1H NMR (300 MHz,
acetone-d6) d: 8.01 (2H, d, J=8.4 Hz), 7.57 (2H, d,
J=8.4 Hz), 7.40 (1H, dd, J=2.0, 8.3 Hz), 7.35±d67.25
(4H, m), 7.17 (1H, d, J=2.0 Hz), 6.90 (1H, d,
J=8.3 Hz), 5.77 (1H, s), 2.69 (2H, q, J=7.6 Hz), 1.49
(6H, s), 1.24 (2H, t, J=7.6 Hz); 13C NMR (75.5 MHz,
acetone-d6) d: 167.0, 155.2, 145.0, 135.9, 134.5, 133.7,
132.1, 130.7, 130.5, 129.4, 129.3, 128.9, 128.8, 123.5,
118.2, 115.3, 93.1, 87.9, 77.4, 29.1, 27.9, 15.9.
Ethyl 2-¯uoro-4-[[4-(4-ethylphenyl)-2,2-dimethyl-(2H)-
chromen-6-yl]-ethynyl]-benzoate (78). Following general
4-[[4-(4-(1-Methylethyl)phenyl)-2,2-dimethyl-(2H)-chro-
men-6-yl]-ethynyl]-benzoic acid (82). Following general

A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
1337
procedure and 75 (95.0 mg, 0.210 mmol) in 3.0 mL THF
and 3.0 mL EtOH, and NaOH (120.0 mg, 3.0 mmol,
3.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 75.0 mg (84%)
the title compound as a colorless solid. 1H NMR
(300 MHz, CDCl3) d: 8.05 (2H, d, J=8.4 Hz), 7.55 (2H,
d, J=8.4 Hz), 7.36 (1H, dd, J=2.0, 8.3 Hz), 7.30±7.26
(5H, m), 6.88 (1H, d, J=8.3 Hz), 5.64 (1H, s), 2.98 (1H,
hept, J=6.9 Hz), 1.51 (6H, s), 1.31 (6H, d, J=6.9 Hz);
13C NMR (75.5 MHz, CDCl3) d: 171.3, 154.2, 148.7,
135.2, 134.0, 133.0, 131.4, 130.1, 129.5, 129.3, 129.0,
128.6, 128.1, 126.6, 122.6, 117.2, 114.2, 93.5, 87.1, 33.9,
27.8, 24.0. Anal. calcd for C29H26O3: C, 82.44; H, 6.20.
Found: C, 82.25; H, 6.28.
J=258.9 Hz), 155.5, 145.0, 135.9, 134.4, 133.9, 133.3,
130.7, 130.6 (d, J=11.7 Hz), 129.4, 129.3, 128.9, 127.8
(d, J=3.8 Hz), 123.5, 120.0 (d, J=24.2 Hz), 118.2,
114.8, 94.1, 86.7 (d, J=2.3 Hz), 77.5, 29.1, 27.9, 15.9.
Anal. calcd for C28H23FO3: C, 78.86; H, 5.44. Found:
C, 78.58; H, 5.35.
Biological assays
RAR binding assay. Each receptor subtype was expres-
sed in Baculovirus. Stock solutions of all compounds
were prepared as 10 mM ethanol solutions and serial
dilutions carried out into 1/1 DMSO/glycerol, 120 mM
KCl, 8 mM Tris, 5 mM CHAPS, 4 mM DTT, and
0.24 mM PMSF, at PH 7.4 at room temperature. The
®nal assay volume was 250 mL and contained 10±40 mg
of protein extract along with 5 nM of [3H] all-trans
retinoic acid and varying concentrations of competing
ligand that ranged from 10 10±10 5 M. The assays were
run using a Biomek formatted for a 96-well minitube
system. Incubations were carried out at 4 ꢀC until equi-
librium was achieved. Nonspeci®c binding was de®ned
as that binding remaining in the presence of 1000 nM of
unlabeled RA. At the end of the incubation period,
50 mL of 6.25% hydroxyapitite was added in a wash
bu€er which consisted of 100 nM KCl, 10 mM Tris, and
0.5% Triton X-100. The mixture was vortexed and
incubated for 10 min at 4 ꢀC, centrifuged and the super-
natant removed. The hydroxyapitite was washed three
more times with the bu€er and the amount of receptor±
ligand complex determined by liquid scintillation
counting of the pellet.
4-[[4-(4-(1,1-Dimethylethyl)phenyl)-2,2-dimethyl-(2H)-
chromen-6-yl]-ethynyl]-benzoic acid (83). Following gen-
eral procedure and 76 (72.0 mg, 0.155 mmol) in 3.0 mL
THF and 3.0 mL EtOH, and NaOH (120.0 mg,
3.0 mmol, 3.0 mL of a 1 M aqueous solution). The resi-
dual solid was recrystallized from CH3CN to give
50.0 mg (74%) the title compound as a colorless solid.
1H NMR (300 MHz, acetone-d6) d: 8.00 (2H, d,
J=8.3 Hz), 7.57 (2H, d, J=8.3 Hz), 7.51 (2H, d, J=
8.3 Hz), 7.41 (1H, dd, J=2.0, 8.3 Hz), 7.31 (2H, d, J=
8.3 Hz), 7.19 (1H, d, J=2.0 Hz), 6.91 (1H, d, J=8.3 Hz),
5.78 (1H, s), 1.49 (6H, s), 1.35 (9H, s); 13C NMR
(75.5 MHz, acetone-d6) d: 167.0, 155.2, 151.8, 135.7,
134.4, 133.8, 132.1, 130.8, 130.7, 130.5, 129.3, 129.1,
128.8, 126.3, 123.4, 118.2, 115.3, 93.1, 87.9, 77.4, 35.2,
31.6, 29.0, 27.9. Anal. calcd for C30H28O3: C, 82.54; H,
6.46. Found: C, 82.29; H, 6.59.
2-Fluoro-4-[[4-(4-methylphenyl)-2,2-dimethyl-(2H)-chro-
men-6-yl]-ethynyl]-benzoic acid (84). Following general
procedure and 77 (60.0 mg, 0.136 mmol) in 2.0 mL THF
and 1.0 mL EtOH, and NaOH (120.0 mg, 3.0 mmol,
3.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 53.0 mg (94%)
the title compound as a colorless solid. 1H NMR
(300 MHz, acetone-d6) d: 7.93 (1H, d, J=7.8 Hz), 7.43±
7.16 (8H, m), 6.91 (1H, d, J=8.3 Hz), 5.77 (1H, s), 2.38
(3H, s), 1.49 (6H, s); 13C NMR (75.5 MHz, acetone-d6)
d: 164.6 (d, J=3.3 Hz), 162.5 (d, J=259.4 Hz), 155.5,
138.6, 135.6, 134.4, 133.9, 133.3, 130.7, 130.6 (d, J=
8.1 Hz), 130.1, 129.5, 129.3, 127.8 (d, J=3.5 Hz), 123.5,
120.0 (d, J=14.6 Hz), 119.2 (d, J=10.5 Hz), 118.2,
114.8, 94.1, 86.7 (d, J=2.7 Hz), 77.5, 27.9, 21.2. Anal.
calcd for C27H21FO3: C, 78.63; H, 5.13. Found: C,
78.49; H, 5.13.
After correcting for nonspeci®c binding, IC50 values
were determined graphically from a log-logit plot of the
data. The Kd values were determined by application of
the Cheng±Prussof equation24 to the IC50 values, the
labeled ligand concentration, and the Kd of the labeled
ligand.
Cotransfection transactivation assay. Eukaryotic expres-
sion vectors pRShRARa,25 pRShRARb,26 pRSh
RARg,26 were cotransfected with the D-MTV-luc
reporter plasmid containing two copies of the TRE-
palindromic response element27 into green monkey CV-
1 cells using calcium phosphate precipitation.28 After
18 h of retinoid treatment the cells were harvested in
0.1 M KPO4 (pH 7.8), 1.0% Triton X-100, 1.0 mM
DTT, and 2 mM EDTA, and analyzed for luciferase
activity as previously described.29
2-Fluoro-4-[[4-(4-ethylphenyl)-2,2-dimethyl-(2H)-chromen-
6-yl]-ethynyl]-benzoic acid (85). Following general pro-
cedure B and 78 (82.0 mg, 0.180 mmol) in 2.0 mL THF
and 2.0 mL EtOH, and NaOH (120.0 mg, 3.0 mmol,
3.0 mL of a 1 M aqueous solution). The residual solid
was recrystallized from CH3CN to give 70.0 mg (91%)
the title compound as a pale-yellow solid. 1H NMR
(300 MHz, acetone-d6) d: 7.93 (1H, d, J=7.8 Hz), 7.41
(1H, dd, J=2.1, 8.3 Hz), 7.37±7.25 (6H, m), 7.18 (1H, d,
J=2.0 Hz), 6.91 (1H, d, J=8.3 Hz), 5.77 (1H, s), 2.69
(2H, q, J=7.6 Hz), 1.49 (6H, s), 1.24 (3H, t, J=7.6 Hz);
13C NMR (75.5 MHz, acetone-d6) d: 164.6, 162.4 (d,
Antagonist assay. To test the ability of the compounds
to function as RAR antagonists in vitro, the trans-
activation assays were repeated in the presence of a
constant dose of the RAR agonist TTNPB=(Ro 13-
7410), (E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-
2-naphthyl)propen-1-yl] benzoic acid. The concentration
used at RARa=3.2Â10 8 M, RARb=1.0Â10 8 M,
and RARg=3.2Â10 9 M. In each experiment the
reference compound AGN 193109 (8) was included in
order to determine the relative potency of the test com-
pound where Relative Potency=IC50(test compound)/
IC50 (8).

1338
A. T. Johnson et al. / Bioorg. Med. Chem. 7 (1999) 1321±1338
14, 287. (b) Kooistra, T.; Lansink, M.; Arts, J.; Sitter, T.;
Acknowledgements
Toet, K. Eur. J. Biochem. 1995, 232, 425. (c) Jing, Y.; Zhang,
J.; Waxman, S.; Mira-y-Lopez, R. Di€erentiation 1996, 60,
109. (d) Standeven, A. M.; Teng, M.; Chandraratna, R. A. S.
Toxicol. Lett. 1997, 92, 231. (e) Kochhar, D. M.; Jiang, H.;
Penner, J. D.; Johnson, A. T.; Chandraratna, R. A. S. Int. J.
Dev. Biol. 1998, 42, 601.
10. (a) Standeven, A. M.; Johnson, A. T.; Escobar, M.;
Chandraratna, R. A. S. Toxicol. Appl. Pharmacol. 1996, 138,
169. (b) Standeven, A. M.; Davies, P. J. A.; Chandraratna, R.
A. S.; Mader, D. R.; Johnson, A. T.; Thomazy, V. A. Fundam.
Appl. Toxicol. 1996, 34, 91.
The authors thank D. Mais and K. Flatten for provid-
ing the ligand binding data, and G. Crosten for the data
from the transactivation assays.
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