The SAR analysis of TRPV1 agonists with the α-methylated B-region

Article abstract of DOI:10.1016/j.bmcl.2012.06.059

A series of TRPV1 agonists with amide, reverse amide, and thiourea groups in the B-region and their corresponding α-methylated analogues were investigated. Whereas the α-methylation of the amide B-region enhanced the binding affinities and potencies as agonists, that of the reverse amide and thiourea led to a reduction in receptor affinity. The analysis indicated that proper hydrogen bonding as well as steric effects in the B-region are critical for receptor binding.

Full text of DOI:10.1016/j.bmcl.2012.06.059

Bioorganic & Medicinal Chemistry Letters 22 (2012) 5227–5231
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
The SAR analysis of TRPV1 agonists with the
a
-methylated B-region
Yongsung Cho a, Myeong Seop Kim a, Ho Shin Kim a, Jihyae Ann a, Jiyoun Lee b, Larry V. Pearce c,
Vladimir A. Pavlyukovets c, Matthew A. Morgan c, Peter M. Blumberg c, Jeewoo Lee a,
⇑
a Research Institute of Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul 151-742, Republic of Korea
b Department of Global Medical Science, Sungshin Women’s University, Seoul 142-732, Republic of Korea
c Laboratory of Cancer Biology and Genetics, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of TRPV1 agonists with amide, reverse amide, and thiourea groups in the B-region and their
corresponding -methylated analogues were investigated. Whereas the -methylation of the amide
B-region enhanced the binding affinities and potencies as agonists, that of the reverse amide and thiourea
led to a reduction in receptor affinity. The analysis indicated that proper hydrogen bonding as well as ste-
ric effects in the B-region are critical for receptor binding.
Received 4 June 2012
Revised 18 June 2012
Accepted 19 June 2012
Available online 23 June 2012
a
a
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Vanilloid receptor 1
TRPV1 agonist
Capsaicin
The transient receptor potential V 1 (TRPV1) is a molecular inte-
grator of nociceptive stimuli expressed predominantly on unmyeli-
nated pain-sensing nerve fibers (C-fibers) and small A d fibers in
the dorsal root, trigeminal, and nodose ganglia.1–3 TRPV1 is struc-
turally a homotetramer and functions as a non-selective cation
channel with high Ca2+ permeability. The receptor is activated
not only by protons,4 heat,5 and endogenous substances such as
anandamide6 and lipoxygenase products7 but also by natural vanil-
loids such as capsaicin (CAP)8 and resiniferatoxin (RTX)9 or indi-
rectly by bradykinin.10 The activation of TRPV1 by these agents
leads to an increase in intracellular Ca2+ resulting in excitation of
the primary sensory neurons. The functional blockade of this
receptor, by antagonism or by desensitization subsequent to
stimulation by agonists, promises considerable therapeutic utility
targeting inflammatory and neuropathic pain, cystitis, and bladder
hyperreflexia.11–15
Naturally found TRPV1 ligands, resiniferatoxin (RTX) and capsa-
icin (Fig. 1), have a vanilloid moiety (A-region) that is connected
through either an ester linkage or amide bond (B-region) to a diter-
pene moiety or a long alkyl chain (C-region), respectively.16 Recent
SAR studies indicated that the modification of the A-region, espe-
cially the modification of the 4-hydroxyl group, led to a complete
loss of agonistic activity,18 and replacing the B-region linkage with
a reverse amide, hydroxamate or thiourea altered the potency.19
Previously we have reported that the A-region derivatives of
effort to investigate the SAR of TRPV1 agonists based on the A-, B-
and C-regions, we have synthesized, based on our lead agonists (1
and 2), a series of TRPV1 agonists bearing amide, reverse amide
and thiourea B-regions togetherwiththeir corresponding
a-methyl-
ated analogues in the B-region, and we have analyzed the effect of
a
-
methylation on receptor affinity and agonist potency. We describe
here the syntheses and functional TRPV1 activities of the designed
ligands and the SAR analysis of the B-region.
The syntheses of the 3-substituted N-(4-t-butylbenzyl)-(4-
hydroxyphenyl)acetamide/propionamide analogues were started
from commercially available 3-substituted-4-hydroxyphenyl acetic
acids 3a–c (Scheme 1). The acetamides 4b–c were prepared from
3b–c, respectively, by the coupling with 4-t-butylbenzylamine.
Dibenzylation of 3 followed by alkylation using LHMDS and methyl
iodide afforded 5. Compound 5a was debenzylated and then cou-
pled with the amine to provide the 3-methoxy propanamide 8a.
On the other hand, compounds 5b–c were hydrolyzed to the acids
7 under basic conditions; the acids were then coupled with the
amine and subsequently deprotected to provide the 3-halo propi-
onamides 8b–c, respectively.
The 4-aminoethoxy acetamides 10a–c were prepared from
3-substituted 4-hydroxyphenyl acetamides (1, 4b–c) in three steps
(Scheme 2). The 2-azidoethoxy group was introduced by the alkyl-
ation of the 4-hydroxyl group with 1-bromo-2-chloroethane and
the subsequent displacement reaction with sodium azide to give
9. The azide group of 9 was reduced by either Staudinger reduction
or hydrogenation to yield the final amines 10a–c.
TRPV1 antagonists with an a-methyl group demonstrated enhanced
binding affinity and potent antagonism for TRPV1.17 As a continuing
The 4-aminoethoxy propanamides 14a–c were prepared from
4-hydroxy intermediates 11 in the same manner as shown in
Scheme 2 (Scheme 3).
⇑
Corresponding author.
E-mail address: jeewoo@snu.ac.kr (J. Lee).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.06.059

5228
Y. Cho et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5227–5231
O
O
H
O
H
O
OH
O
O
OCH3
OH
OCH3
OH
N
H
O
Resiniferatoxin
Capsaicin
S
H
N
OCH3
OH
OCH3
OH
N
H
N
H
O
2
1
Figure 1. TRPV1 agonists.
HO
X
BnO
X
HO
X
a,b
c
O
O
O
X=F,Cl
OH
OBn
OBn
5a-c
7b-c
d,e
3a X=OCH3
3b X=F
3c X=Cl
X=OCH3
O
d
e
HO
X
H
N
H
N
X
d
X
OH
O
O
OH
OH
1
X=OCH3
6
8a X=OCH3
8b X=F
4b X=F
4c X=Cl
8c X=Cl
Scheme 1. Reagents and conditions: (a) BnBr, K2CO3, acetone, reflux, 15 h, 98–99%; (b) LHMDS, CH3I, THF, À78 °C, 30 min, 68–70%; (c) LiOH, THF-H2O, rt, 15 h, 90–92%; (d)
4-t-butylbenzylamine, EDC, DMAP or HOBt, CH2Cl2, rt, 15 h, 52–80%; (e) Pd/C, H2, CH3OH, rt, 1 h, 70% for X = OCH3 and 55% for X = F: 1 M BCl3 in CH2Cl2, À78 °C, 62% for X = Cl.
H
N
H
N
1
a,b
X
c
X
4b
4c
O
NH2
O
N3
O
O
10a X=OCH3
10b X=F
9
10c X=Cl
Scheme 2. Reagents and conditions: (a) 1,2-dibromoethane, 40% KOH, Bu4NOH, 93% for X = OCH3: 1-bromo-2-chloroethane, K2CO3, acetone, reflux, 49–60% for X = F, Cl; (b)
NaN3, TBAB, KI, toluene, reflux, 71–80%; (c) PPh3, H2O, THF, 14% for Cl and 58% for X = OCH3: Pd/C, H2, CH3OH, rt, 6 h, 38% for X = F.
The C-region analogues of acetamide/propionamide were pre-
pared from the acid intermediates (3a, 6 and 13a) by the coupling
with the corresponding amines to yield the final compounds 18–
25 (Scheme 4).
The binding affinities and agonistic/antagonistic functional
activities of the synthesized TRPV1 ligands were determined
in vitro by a binding competition assay with [3H]RTX and a func-
tional 45Ca2+ uptake assay using rat TRPV1 heterologously ex-
pressed in Chinese hamster ovary (CHO) cells, as previously
described.20 The results are summarized in Tables 1–4, together
with the potencies of the parent agonists 1 and 2.
The reverse amide analogues were synthesized from the ben-
zylamine 23 or
a-methyl benzylamine 28, which was prepared
from 4-hydroxy-3-methoxy acetophenone by reductive amination
(Scheme 5). The coupling reactions of above benzylamines with
commercially available fatty acids provided the C-region analogues
In order to investigate how the introduction of an
a-methyl
group into the B-region of agonists affects their TRPV1 binding
and functional activity as compared to that of the parent com-
pounds, we first fixed the C-region as a 4-tert-butylbenzyl moiety
and varied the A-region functionality (Table 1). Compound 8a, an
with reverse amide 24–36 and
-Methyl thiourea analogue 32 was also prepared from 28 by the
coupling with 4-t-butylbenzyl isothiocyanate.
The 4-aminoethoxy thiourea 34 and its -methyl analogue 36
a-methyl reverse amide 29–31.
a
a
a-methylated analogue of the parent agonist (1), showed enhanced
were readily synthesized from the corresponding benzylamines
23 and 28 by following the routes described in Schemes 3 and 5,
respectively (Scheme 6).
binding affinity and agonism by 2- and 3-fold, respectively. When
we replaced the 3-methoxy group with halides to provide 8b and
8c, these analogues bound TRPV1 even more tightly (Ki = 178 nM

Y. Cho et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5227–5231
5229
EtO
X
EtO
X
a
b,c
3
O
N3
O
O
OH
12
11
d,e
H
N
X
HO
X
f,g
O
NH2
O
N3
O
O
14a X=OCH3
14b X=F
13
14c X=Cl
Scheme 3. Reagents and conditions: (a) cat. H2SO4, EtOH, reflux, 98–99%; (b) 1-bromo-2-chloroethane, K2CO3, acetone, reflux, 55–65%; (c) NaN3, TBAB, KI, toluene, reflux, 6 h,
90–95%; (d) NaH, CH3I, DMF, 0 °C, 1 h, 65–75%; (e) NaOH, H2O, reflux, 2 h, 98–99%; (f) 4-tert-butylbenzylamine, EDC, DMAP, CH2Cl2, rt, 15 h, 70–74%; (g) Pd/C, H2, CH3OH, rt,
80–85%.
R1
R1
H
N
HO
OCH3
OR2
OCH3
OR2
a
R3
O
O
3a R1=H, R2=H
R1=CH3, R2=H
13a R1=CH3, R2=CH2CH2N3
15 R1=H, R2=H, R3=(CH2)7CH3
6
16 R1=H, R2=H, R3=(CH2)8CH3
17 R1=H, R2=H, R3=3,4-Me2Ph(CH2)3
18 R1=CH3, R2=H, R3=(CH2)7CH3
19 R1=CH3, R2=H, R3=(CH2)8CH3
20 R1=CH3, R2=H, R3=3,4-Me2Ph(CH2)3
21 R1=CH3, R2=CH2CH2N3, R3=3,4-Me2Ph(CH2)3
22 R1=CH3, R2=CH2CH2NH2, R3=3,4-Me2Ph(CH2)3
b
Scheme 4. Reagents and conditions: (a) EDC, DMAP, DMF, rt, 15 h, 70–80%; (b) Pd/C, H2, CH3OH, rt, 80%.
O
R1
OCH3
OH
OCH3
OH
H2N
a
R2
N
H
23
24 R1=H, R2=CH3(CH2)7CH=CH(CH2)7
25 R1=H, R2=CH3(CH2)7
26 R1=H, R2=CH3(CH2)8
O
R1
OCH3
OH
OCH3
OH
OCH3
OH
b,c
a
O
H2N
R2
N
H
27
28
29 R1=CH3, R2=CH3(CH2)7CH=CH(CH2)7
30 R1=CH3, R2=CH3(CH2)7
d
31 R1=CH3, R2=CH3(CH2)8
S
OCH3
OH
N
H
N
H
32
Scheme 5. Reagents and conditions: (a) RNH2, EDC, DMAP, Et3N, DMF, rt, 15 h, 65–70%; (b) NH2OHÁHCl, Pyridine, CH2Cl2, reflux, 95%; (c) Pd/C, conc.ÁHCl, MeOH, rt, 15 h, 90%;
(d) 4-t-butylbenzyl isothiocyanate, NEt3, CH2Cl2, rt, 60%.
for 8b, Ki = 33 nM for 8c) and their affinities increased ca. 4.5- and
4-fold compared to 4b and 4c, respectively. However, their func-
tional activity shifted towards partial agonism/partial antagonism
(as most evident for the decreased level of agonism of 8c). The
SAR pattern in which the halogenations in the A-region shifted
the functional activity to antagonism, with increased antagonism
as the size of the halogen increased, was established in our previ-
ous report.21
also examined the effect of a-methylation on the 2-aminoethoxy
analogues of the amide agonists. Although all 4-aminoethoxy ana-
logues synthesized were found to be partial agonists/antagonists,
the binding affinities of
a-methylated analogues 14a–c increased
significantly compared to the acetamides 10a–c by 2.5- to 6.5-fold,
respectively.
Next, we swapped the 4-tert-butylbenzyl group of 1 with long
alkyl and arylalkyl chains, resembling the C-region of capsaicin, to
Previously, we reported that 2-aminoethylation of the 4-hydro-
xyl group in the capsainoid improved in vivo stability as well as
analgesic activity compared to the parent agonist.22 Thereby, we
provide 15–17 and examined the effect of their
(Table 2). Whereas the -methylation of acetamide 15 did not af-
fect its receptor activity, -methylated analogues 19 and 20
a-methylation
a
a

5230
Y. Cho et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5227–5231
S
OCH3
OCH3
O
a-d
g-k
e,f
H2N
N
H
N
H
23
28
N3
NH2
NH2
O
34
33
35
S
OCH3
O
OCH3
O
e,l
N
H
N
H
H2N
NHBoc
36
Scheme 6. Reagents and conditions: (a) (Boc)2O, NEt3, H2O-Dioxane, rt, 2 h, 99%; (b) 1,2-dibromoethane, 40% KOH, Bu4NOH, 50 °C, 2 h, 90%; (c) NaN3, DMF, 100 °C, 15 h, 74%;
(d) TFA,CH2Cl2, 0 °C, 5 h; (e) 4-tert-butylbenzyl isothiocyanate, NEt3, CH2Cl2, rt, 15 h, 60%; (f) PPh3, H2O, THF, 99%; (g) 1-bromo-2-chloroethane, K2CO3, acetone, reflux, 3 h,
94%; (h) NaN3, TBAB, KI, toluene, reflux, 99%; (i) (Boc)2O, Pd/C, H2, EtOH, rt; (j) NH2OHÁHCl, pyridine, 80 °C, 2 h; (k) Pd/C, H2, conc. HCl, EtOH, rt, 15 h; (l) TFA, CH2Cl2, 0 °C, 1 h,
55%; PPh3, H2O, THF, 99%.
Table 1
Amide B-region with 4-t-butylbenzyl C-region
R
H
N
R2
O
OR1
R
R1
R2
Ki (nM) binding affinity
EC50 (nM) agonism
Ki (nM) antagonism
1
4b
4c
8a
8b
8c
10a
10b
10c
14a
14b
14c
H
H
H
CH3
CH3
CH3
H
H
H
H
H
H
H
H
H
OCH3
F
Cl
OCH3
F
Cl
OCH3
F
Cl
667 ( 86)
808 ( 179)
132 ( 29)
308 ( 7.0)
178 ( 33)
33.1 ( 6.6)
1230 ( 230)
10,100 ( 1300)
2470 ( 490)
504 ( 160)
2160 ( 410)
380 ( 110)
82 ( 34)
911 ( 88)
206 ( 41)
24 ( 6.4)
221 ( 63)
(77%)a
NE
(30%)b
NE
(15%)b
(20%)b
(9%)b
(12%)b
(18%)b
(56%)b
(16%)b
NE
CH2CH2NH2
CH2CH2NH2
CH2CH2NH2
CH2CH2NH2
CH2CH2NH2
CH2CH2NH2
358 ( 58)
(63%)a
(36%)a
CH3
CH3
CH3
OCH3
F
Cl
238 ( 79)
(91%)a
(75%)a
(38%)b
A
B
Only fractional calcium uptake compared with that induced by 300 nM capsaicin.
Only fractional antagonism at 30 M.
l
Table 2
Amide B-region with alkyl and arylalkyl C-region
R2
H
N
R3
OCH3
OR1
O
R1
R2
R3
Ki (nM) binding affinity
EC50 (nM) agonism
Ki (nM) antagonism
15
16
17
18
19
20
DA-5018
22
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
H
(CH2)7CH3
(CH2)8CH3
(CH2)3Ph(3,4-Me2)
(CH2)7CH3
848 ( 67)
240 ( 43)
354 ( 84)
744 ( 32)
159 ( 22)
177 ( 30)
930 ( 170)
518 ( 110)
77 ( 18)
61 ( 16)
41 ( 26)
130 ( 16)
26.3 ( 7.6)
21.3 ( 2.7)
589 ( 76)
404 ( 67)
NE
NE
NE
NE
NE
NE
NE
NE
(CH2)8CH3
(CH2)3Ph(3,4-Me2)
(CH2)3Ph(3,4-Me2)
(CH2)3Ph(3,4-Me2)
CH2CH2NH2
CH2CH2NH2
CH3
showed a 1.5- to 2-fold enhancement in binding affinity and
To further evaluate the effect of a-methylation in the B-region,
agonism compared to 16 (nonivamide) and 17. DA-5018 is the
we also investigated the reverse amide (Table 3) and thiourea B-re-
2-aminoethyl analogue of 17. The
generate 22 likewise led to ca. 2-fold increase in receptor activity.
The results indicated that -methylation in the amide B-region
might enhance favorable hydrogen bonding with the receptor or
provide an additional hydrophobic interaction of a methyl group
with the receptor.
a-methylation of DA-5018 to
gions (Table 4) in a similar fashion. The reverse amide B-region
agonists olvanil 24 and 25–26 and their
29–30 were prepared for the comparison of receptor activities.
The analysis indicated that -methylation in the reverse amide
a-methylated analogues
a
a
B-region led to a decrease in receptor activity in which 29–31
showed 2- to 4- fold reductions in binding affinity compared to

Y. Cho et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5227–5231
5231
Table 3
Reverse amide B-region with alkyl C-region
O
R1
OCH3
OH
R2
N
H
R1
R2
Ki (nM) binding affinity
EC50 (nM) agonism
Ki (nM) antagonism
24 (Olvanil)
H
H
H
CH3
CH3
CH3
(CH2)7CH@CH(CH2)7CH3
(CH2)7CH3
(CH2)8CH3
(CH2)7CH@CH(CH2)7CH3
(CH2)7CH3
(CH2)8CH3
142 ( 27)
1223 ( 18)
864 ( 10)
226 ( 52)
4275 ( 99)
3300 ( 610)
202 ( 19)
223 ( 47)
83 ( 16)
678 ( 140)
1580 ( 290)a
1250 ( 140)
NE
NE
NE
NE
25
26
29
30
31
(44%)b
(28%)b
A
B
Only fractional calcium uptake (72%) compared with that induced by 300 nM capsaicin.
Only fractional antagonism at 30 M.
l
Table 4
Thiourea B-region with 4-t-butylbenzyl C-region
S
R2
OCH3
OR1
*
N
H
N
H
R1
R2
Ki (nM) binding affinity
EC50 (nM) agonism
Ki (nM) antagonism
2
H
H
H
CH3
H
59 ( 9.0)
194 ( 5)
84 ( 27)
2.6 ( 1.1)
NE
32
34
36
380 ( 160)a
132 ( 34)
(35%)b
NE
CH2CH2NH2
CH2CH2NH2
CH3
1430 ( 520)
5800 ( 1700)
NE
A
B
Only fractional calcium uptake (70%) compared with that induced by 300 nM capsaicin.
Only fractional antagonism at 30 M.
l
the corresponding acetamides. The similar SAR pattern was also
observed in the thiourea B-region. The -methylated thioureas
32 and 36 showed marked loss of binding affinity compared to 2
and 34 by 3- and 17-fold. The result indicated that, different from
References and notes
a
1. Szallasi, A.; Blumberg, P. M. Pharmacol. Rev. 1999, 51, 159.
2. Nagy, I.; Santha, P.; Jancso, G.; Urban, L. Eur. J. Pharmacol. 2004, 500, 351.
3. Alawi, K.; Keeble, J. Pharmacol. Ther. 2010, 125, 181.
4. Tominaga, M.; Caterina, M. J.; Malmberg, A. B.; Rosen, T. A.; Gilbert, H.; Skinner,
K.; Raumann, B. E.; Basbaum, A. I.; Julius, D. Neuron 1998, 21, 531.
5. Caterina, M. J.; Schumacher, M. A.; Tominaga, M.; Rosen, T. A.; Levine, J. D.;
Julius, D. Nature 1997, 389, 816.
6. Zygmunt, P. M.; Petersson, J.; Andersson, D. A.; Chuang, H.; Sorgard, M.; Di
Marzo, V.; Julius, D.; Hogestatt, E. D. Nature 1999, 400, 452.
7. Hwang, S. W.; Cho, H.; Kwak, J.; Lee, S. Y.; Kang, C. J.; Jung, J.; Cho, S.; Min, K. H.;
Suh, Y. G.; Kim, D.; Oh, U. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 6155.
8. Walpole, C. S.; Wrigglesworth, J. R. Capsaicin in the study of pain; Academic
Press: San Diego, CA, 1993.
9. Appendino, G.; Szallasi, A. Life Sci. 1997, 60, 681.
10. Julius, D.; Basbaum, A. I. Nature 2001, 413, 203.
11. Gunthorpe, M. J.; Chizh, B. A. Drug Discovery Today 2009, 14, 56.
12. Wong, G. Y.; Gavva, N. R. Brain Res. Rev. 2009, 60, 267.
13. Szallasi, A.; Cortright, D. N.; Blum, C. A.; Eid, S. R. Nat. Rev. Drug Disc. 2007, 6, 357.
14. Westaway, S. M. J. Med. Chem. 2007, 50, 2589.
the amide B-region, the
a-methylation of the reverse amide and
thiourea might interfere with appropriate hydrogen bonding with
the receptor due to steric hindrance.
In summary, we have synthesized a series of TRPV1 agonists
with the amide, reverse amide, and thiourea groups in the B-re-
gion along with their corresponding
a-methylated analogues.
Within the amide analogues, the -methylation enhanced binding
a
affinity and agonism compared to the parent agonist due to favor-
able hydrogen bonding interaction or additional hydrophobic
interaction of a methyl in the binding site. By contrast, the
a-
methylation of the reverse amide and thiourea agonists led to
the reduction in receptor activity, suggesting that the placement
of a methyl group might interfere with appropriate hydrogen
bonding with the receptor due to steric hindrance. The SAR anal-
15. Krause, J. E.; Chenard, B. L.; Cortright, D. N. Curr. Opin. Investig. Drugs 2005, 6, 48.
16. Conway, S. J. Chem. Soc. Rev. 2008, 37, 1530.
17. Kim, Y. S.; Kil, M. J.; Kang, S. U.; Ryu, H.; Kim, M. S.; Cho, Y.; Bhondwe, R. S.;
Thorat, S. A.; Sun, W.; Liu, K.; Lee, J. H.; Choi, S.; Pearce, L. V.; Pavlyukovets, V.
A.; Morgan, M. A.; Tran, R.; Lazar, J.; Blumberg, P. M.; Lee, J. Bioorg. Med. Chem.
2012, 20, 215.
ysis of
steric effect in the B-region as critical for receptor binding. The
SAR of the two enantiomers of the -methylated amide is under-
a-methylation implicates hydrogen bonding as well as a
a
18. Lee, J.; Kang, S. U.; Kil, M. J.; Shin, M.; Lim, J. O.; Choi, H. K.; Jin, M. K.; Kim, S. Y.;
Kim, S. E.; Lee, Y. S.; Min, K. H.; Kim, Y. H.; Ha, H. J.; Tran, R.; Welter, J. D.; Wang,
Y.; Szabo, T.; Pearce, L. V.; Lundberg, D. J.; Toth, A.; Pavlyukovets, V. A.; Morgan,
M. A.; Blumberg, P. M. Bioorg. Med. Chem. Lett. 2005, 15, 4136.
19. Lee, J.; Kang, S. U.; Choi, H. K.; Lim, J. O.; Kil, M. J.; Jin, M. K.; Kim, K. P.; Sung, J.
H.; Chung, S. J.; Ha, H. J.; Kim, Y. H.; Pearce, L. V.; Tran, R.; Lundberg, D. J.; Wang,
Y.; Toth, A.; Blumberg, P. M. Bioorg. Med. Chem. Lett. 2004, 14, 2291.
20. Wang, Y.; Szabo, T.; Welter, J. D.; Toth, A.; Tran, R.; Lee, J.; Kang, S. U.; Suh, Y. G.;
Blumberg, P. M. Mol. Pharmacol. 2002, 62, 947.
21. Kang, D. W.; Kim, Y. S.; Lim, K. S.; Kim, M. S.; Pearce, L. V.; Pavlyukovets, V. A.; Tao,
A. K.; Lang-Kuhs, K. A.; Blumberg, P. M.; Lee, J. Bioorg. Med. Chem. 2010, 18, 8092.
22. Lee, J.; Lee, J.; Kang, M.-S.; Kim, K.-P.; Chung, S.-J.; Blumberg; Lee, J.; Lee, J.;
Kang, M.-S.; Kim, K.-P.; Blumberg, P. M.; Yi, J.-B.; Park, Y. H. Bioorg. Med. Chem.
2002, 10, 1171.
way to further explore interactions with the receptor.
Acknowledgments
This research was supported by Grants R11-2007-107-02001-0
from the NRF and was supported in part by the Intramural Research
Program of the National Institutes of Health, Center for Cancer Re-
search, National Cancer Institute (Project Z1A BC 005270). We thank
other members of the Blumberg group for assistance with some of
the assays.