Synthesis of the PPARβ/δ-selective agonist GW501516 and C4-thiazole-substituted analogs

Article abstract of DOI:10.1016/j.bmcl.2005.09.060

Sequential, position-selective, Pd-catalyzed cross-coupling reactions of 2,4-dibromo-5-hydroxymethylthiazole provided the scaffold for the synthesis of GW501516, the most potent PPARβ/δ agonist yet described, and equally selective analogs at the thiazole-

Full text of DOI:10.1016/j.bmcl.2005.09.060

Bioorganic & Medicinal Chemistry Letters 16 (2006) 49–54
Synthesis of the PPARb/d-selective agonist GW501516
and C4-thiazole-substituted analogs
Raquel Pereira,a Claudine Gaudon,b Beatriz Iglesias,a Pierre Germain,b
Hinrich Gronemeyerb and Angel R. de Leraa,*
aDepartamento de Quı´mica Orga´nica, Universidade de Vigo, 36310 Vigo, Spain
bInstitut de Ge´ne´tique et de Biologie Mole´culaire et Cellulaire (IGBMC)/CNRS/INSERM/ULP, BP 163, 67404 Illkirch Cedex,
C. U. de Strasbourg, France
Received 15 June 2005; revised 20 September 2005; accepted 21 September 2005
Available online 18 October 2005
Abstract—Sequential, position-selective, Pd-catalyzed cross-coupling reactions of 2,4-dibromo-5-hydroxymethylthiazole provided
the scaffold for the synthesis of GW501516, the most potent PPARb/d agonist yet described, and equally selective analogs at the
thiazole-C4 position.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Peroxisome proliferator-activated receptors (PPARs)
are members of the nuclear hormone receptor superfam-
ily.1 Upon activation by a ligand, these proteins act as
transcription factors, regulating multiple physiological
pathways, including reproduction, growth, differentia-
tion, development, energy metabolism, and homeosta-
sis.1b,c The PPAR subfamily comprises three subtypes
(a, c, and b/d) that exhibit different tissue distribution
and physiological functions, serving as dietary lipid sen-
sors for the control of fatty acid and carbohydrate
metabolism.2 PPARa is highly enriched in the liver
and, upon binding its ligands, such as the fibrates, mod-
ulates lipid metabolism. PPARc is mostly expressed in
adipose tissue and activates adipogenesis when bound
to natural [(S)-15-deoxy-D12,14-PGJ2] or synthetic (thia-
zolidinedione or glitazone) ligands. Together, the a and
c subtypes regulate the balance between catabolism and
storage of long-chain fatty acids. Interestingly, the
PPARb/d subtype, widely expressed in brain, colon,
and skin, can be a potent transcriptional repressor,3
inhibiting the ligand-induced transcriptional activity of
the a and c subtypes. The anti-lipid oxidation and
anti-adipogenic role of PPARb/d holds considerable
promise for the therapeutic control of obesity and type
II diabetes through ligand design.3
Compared to the a and c subtypes, relatively few ligands
for PPARb/d have been described.2 In common with the
other subtypes, a variety of polyunsaturated fatty acids
(arachidonic acid, linoleic acid, and eicosapentaenoic
acid) and their metabolites bind PPARb/d at micromo-
lar concentrations, whereas the semisynthetic carba-
prostacyclin shows higher affinity.4 Synthetic ligands
have been discovered which show selectivity for the
b/d subtype, in particular those built around thiazole
and oxazole rings.5 GW501516 1a (Scheme 1) is the
most potent (Ki = 1.1 0.1 nM) and selective (>1000-
fold selective for PPARb/d over the other subtypes)
PPARb/d agonist.3 GW501516 also promotes reverse
cholesterol transport, an effect of potential interest for
the prevention of cardiovascular diseases.3
The synthesis of GW501516 has recently been described6
and consists of a linear sequence in which the thiazole
ring 3 is constructed by a Hantzsch-type condensation of
thiobenzamide 5 and 2-chloroacetoacetate 4 (Scheme 1).
We considered an alternative synthesis that would allow
the incorporation of a variety of substituents on the
thiazole scaffold. To this end, dihalogenated thiazole
derivatives, such as 7 or 11, were selected, with the
purpose of exploiting the differential reactivity of the
Keywords: Thiazoles; Stille reactions; Suzuki reactions; Nuclear recep-
tors; PPAR.
*
Corresponding author. Tel.: +34 986 812316; fax: +34 986 811940;
e-mail: qolera@uvigo.es
0960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.09.060

50
R. Pereira et al. / Bioorg. Med. Chem. Lett. 16 (2006) 49–54
N
N
S
HO
S
S
O
CF3
CF3
2a
1a, GW501516
HO2C
O
S
N
EtO
+
H2N
EtO
S
Cl
O
CF3
CF3
O
3
4
5
Scheme 1.
halogens using palladium-catalyzed cross-coupling reac-
tions7 (Schemes 2 and 3).
thiazolidinedione 6.12 Given the enhanced reactivity
expected at the most electron-deficient C2 position of
7, a metal derivative 8—prepared from commercially
available 4-bromotrifluoromethylbenzene13—for trans-
ferring a 4-trifluoromethylphenyl group was used. How-
ever, under the Suzuki reaction conditions optimized for
the selective coupling of dibromothiophenes,8 boronate
8 [M = B(OMe)2] led to mixtures of mono- (9) and
di-substituted (10) derivatives together with unreacted
starting material. The electron-withdrawing nature of
both the formyl and trifluoromethylphenyl substituents
in the thiazole ring of monosubstituted derivative 9
combines to induce a second coupling at C4 at a rate
which competes with that of 7.
The premise that site-selective reactions of 7 or 11 are
possible was based on previously reported sequential
halogen replacement reactions in (un)substituted
dibromoheteroarenes (thiophenes,8,9 furans,10 and thiaz-
oles11) at the most electron-deficient position. Sequential
replacement of 2,4-dibromothiazole with organozinc
compounds, first at C2 and then at C4, has been descri-
bed.11e The halogen-selective Pd-catalyzed cross-coupling
reaction of 2-bromo-5-chlorothiazole-4-carboxylate has
been described,11g but the site-selective cross-coupling
of a functionalized dibromothiazole is unprecedented.
We show that this approach for building functional
diversity at the thiazole scaffold is indeed feasible, and
describe a new total synthesis of GW501516 as well as
a group of derivatives that incorporate aryl and hetero-
aryl substituents at C4 using commercially available
organometallic compounds.
Position-selective replacement of the bromine at C2 was
achieved on the less electron-deficient hydroxymethyl
dibromothiazole 11,12 using either the Stille or the
Suzuki cross-coupling reactions (Scheme 3) under care-
fully optimized conditions.8 The organotin derivative 8
(M = SnBu3, 1.3 mol equiv) coupled at 70 ꢁC for 24 h
using FarinaÕs catalytic system14 [Pd2(dba)3/AsPh3 as
palladium source/ligand combination in NMP] to
The required 2,4-dibromo-5-formylthiazole 7, Scheme 2,
can be readily prepared from commercially available
(MeO)2B
R
Br
N
O
8
CF3
POBr3
N
H
NH
S
H
DMF, 72%
Br
Pd(PPh3)4, K2CO3
PhMe, 25 ˚C to 50 ˚C
O
CF3
S
O
S
O
6
7
9, R = Br
10, R =
CF3
Scheme 2.
F3C
Br
N
Br
N
HO
+
N
+
M
CF3
S
HO
HO
Br
S
S
CF3
CF3
11
8
12
13
Scheme 3.

R. Pereira et al. / Bioorg. Med. Chem. Lett. 16 (2006) 49–54
51
provide derivative 12 in 68% yield. Increasing the reac-
tion temperature to 90 ꢁC led to erosion of selectivity
converted into the corresponding chlorides 15 using
MsCl and Et3N. Substitution of the chloride by aryl thi-
ols 166 and 226b (Scheme 6) using Cs2CO3 in CH3CN
proceeded at room temperature to give esters 17a,17
17b, 17d, 23a, 23b, and 23d. However, the vinyl deriva-
tives 17c and 23c could not be isolated. Reaction of 15c
led to a complex mixture including ester 17c, which may
be present in an approximate 45% yield, as estimated by
1H NMR, thiol 16, or its disulfide derivative, and the
product of addition of the thiol to the vinyl group, 18.
Only the addition product 18 could be isolated from this
mixture in 20% yield. Its formation during the reaction
course is not totally unexpected due to the known prece-
dents for the addition of thiols onto carbon–carbon
double bonds in the presence or absence of an acidic
catalyst.18
(71:29 12/13). The Suzuki reaction with
8
[M = B(OMe)2, 1.3 mol equiv] [Pd(PPh3)4, K2CO3, tolu-
ene]15 required a higher temperature (100 ꢁC) but the
selectivity was also complete (87% yield).16
For the second metal-catalyzed coupling, more forcing
reaction conditions were required (Scheme 4, Table 1)
to reach completion. The Stille reaction was optimized
for coupling 12 with tetramethyltin 14a (entry 1, 70%),
tri-n-butyl-2-furyltin 14b (entry 3, 70%), and tri-n-butyl-
vinyltin 14c (entry 6, 69%), whereas Suzuki cross-cou-
pling served well for the reaction with phenylboronic
acid 14d (entry 8, 78%), to furnish the trisubstituted
thiazoles 2a–d, respectively. NOE experiments at this
stage in derivative 2a revealed the proximity of the
methyl and methylene substituents, thus supporting
the anticipated outcome of the sequential cross-coupling
reactions.
The synthetic route was completed with the saponifica-
tion of esters 17 and 23 with potassium carbonate to
afford the desired targets 1a,17 1b, 1d, 24a, 24b, and 24d.
The synthesis of GW501516 and its C4-substituted ana-
logs was completed as shown in Scheme 5, following
the previously described protocol.6b Alcohols 2 were
The transcriptional activity of the newly synthesized
compounds has been investigated using a PPARb/d
ÔreporterÕ cell line and compared to the activity of the
R
Br
N
N
Pd(0)
HO
+
R-M
HO
S
S
CF3
CF3
2a, R = Me
12
14
2b, R = 2-furyl
2c, R = vinyl
2d, R = Ph
Scheme 4.
Table 1. Palladium-catalyzed cross-coupling reactions of bromothiazole 12
Entry
1
R–M (mol equiv)
Me4Sn (2.0)
Reaction conditions
T (ꢁC)
t (h)
2 (%)
12 (%)
PdCl2(PPh3)2 (15%), DMA
140
18
70
0
2
3
Pd2(dba)3 (3%), AsPh3 (20%), NMP
Pd2(dba)3 (3%), AsPh3 (20%), NMP
115
115
17
16
68
7
0
SnBu3
O
(1.5)
70
SnBu3
O
(2.0)
SnBu3
(1.5)
4
5
Pd2(dba)3 (3%), AsPh3 (20%), NMP
Pd2(dba)3 (3%), AsPh3 (20%), NMP
120
120
24
24
24a
18a
49a
52a
SnBu3
(2.2)
SnBu3
(2.2)
6
7
Pd2(dba)3 (7%), AsPh3 (47%), NMP
120
100
20
20
69
47
0
0
SnBu3
(2.2)
Pd2(dba)3 (1.5%), PtBu3 (6%), CsF, dioxane
B(OH)2
8
Pd(PPh3)4 (5%), K2CO3, PhMe
115
16
78
0
(1.5)
a Yield was determined by 1H NMR integration of the mixture.

52
R. Pereira et al. / Bioorg. Med. Chem. Lett. 16 (2006) 49–54
SH
R
R
N
N
R'
S
O
S
S
16
MeO2C
CF3
a
O
CF3
b
2
R' = OH
17 R' = Me
R'O2C
c
15 R' = Cl
1a R = Me, R' = H, GW501516
1b R = 2-furyl, R' = H
1d R = Ph, R' = H
S
18 R' = Me
R =
O
MeO2C
Scheme 5. Reagents: (a) ClSO2Me, Et3N, CH2Cl2; (b) Cs2CO3, CH3CN (17a, 87%; 17b, 75%; 17d, 87%; combined yields); (c) K2CO3, MeOH
(1a, 96%; 1b, 91%; 1d, 92%).
S
S
SH
b
c
a
O
HO
HO
2
2
MeO2C
19
20
21
R
R
N
N
S
Cl
S
S
SH
CF3
e
CF3
O
15
O
23 R' = Me
R'O2C
d
22
MeO2C
24a R = Me, R' = H
24b R = 2-furyl, R' = H
24d R = Ph, R' = H
Scheme 6. Reagents: (a) DMSO (93%); (b) 1—NaH, DMF, 2—BrCH2CO2Me (82%); (c) Zn, HCl 10%, CH2Cl2 (84%); (d) Cs2CO3, CH3CN
(23a, 37%; 23b, 97%; 23d, 69%); (e) K2CO3, MeOH (24a, 97%; 24b, 92%; 24d, 86%).
previously identified potent agonist GW501516 1a. At
high concentrations (10À7 M) all studied compounds
are quite similar in their ability to activate reporter gene
transcription through PPARb/d (Fig. 1). None of the
compounds displayed any detectable activity with either
PPARa or PPARc (data not shown), demonstrating a
PPARb/d selectivity similar to that of GW501516 1a.
Dose–response curves with increasing ligand concentra-
tions were performed to assess the cellular potency of
the compounds to PPARb/d. Similar curves were ob-
tained with GW501516 1a and both its derivatives 1b
and 1d, indicating comparable transcriptional activities
(Fig. 2). However, EC50 derived from our experimental
data indicate that GW501516 1a is slightly more effec-
tive than both 1b and 1d (5 · 10À10, 4 · 10À9, and
2 · 10À9 M, respectively). Series 1 exhibited a higher cel-
lular potency than series 24, because the compounds of
series 24 required, in general, higher concentrations to
attain the same transcriptional outcome as series 1 (see
the right shift of the curves in Fig. 3 compared to
Fig. 2). The EC50 determined for series 24 are
4 · 10À9 M for 24a, 3 · 10À8 M for 24b, and
9 · 10À9 M for 24d. Thus, addition of furyl and phenyl
groups does not significantly affect the potencies of
GW501516 1a and 24a to PPARb/d, whereas removal
of the methyl group in series 1 (converting series 1 into
series 24) provoked a loss of efficacy. Increasing
the bulkiness at the thiazole C4-position by introducing
a phenyl group reduced the agonist activity of the
ligand.
In summary, the potent PPARb/d agonist GW501516 1
and analogs have been synthesized from a trisubstituted
thiazole scaffold 2 itself obtained by position-selective
consecutive palladium-catalyzed cross-coupling reaction
of 2,4-dibromo-5-hydroxymethylthiazole 11 and orga-
nometallic derivatives. Structural variations of the
organometallic components (as shown for the second
cross-coupling) add potential to the synthetic scheme
and lead to a diverse range of thiazole C4-analogs built

R. Pereira et al. / Bioorg. Med. Chem. Lett. 16 (2006) 49–54
53
Figure 1. Transactivation studies were performed to assess PPARb/
d activity of synthetic compounds using stably transfected HeLa
cells expressing chimeric proteins containing the GAL4 DNA-
binding domain fused to the ligand binding domain of PPARb/d
Figure 3. Transactivation studies as in Figure 2. Gal-PPARb/d
reporter cells were incubated with increasing concentrations of 24a
(closed squares), 24b (open diamonds), or 24d (closed circles) for 16 h.
and
a luciferase gene driven by a pentamer of the Gal4
recognition sequence (Ô17 mÕ) in front of the b-globin promoter,
as illustrated at the top. This reporter system is unaffected by the
presence of endogenous receptors as they cannot recognize the
Gal4 binding.19 Cells were incubated with various synthetic
compounds at 0.1 lM.
Acknowledgments
We thank Audrey Bindler for technical assistance, the
European Commission (QLK3-2002-02029 ÔAnticancer
´
RetinoidsÕ), the Spanish Ministerio de Educacion y
Ciencia (Grant SAF04-07131), and FEDER and Xunta
de Galicia (Grant PGIDIT02PXIC30108PN) for finan-
cial support.
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