C. Lamers et al. / Bioorg. Med. Chem. Lett. 24 (2014) 4048–4052
4049
O
OH
S
O
N
N
O
N
OH
O
O
O
O
O
O
O
Aleglitazar
Muraglitazar
S
O
O
O
S
OH
OH
O
O
O
N
O
N
O
O
Saroglitazar
Tesaglitazar
O
O
H
H
N
N
S
N
N
S
OH
OH
N
N
H
Cl
Cl
1
6
,
Pirinixic acid (WY-14,643, MD78
)
Chart 1. Structures of PPARa/c dual agonists.
at PPAR
c
is desirable. Hence the balance between activation of
may determine efficacy and toxicity, especially
PPAR and PPAR
a
c
in the treatment of the metabolic syndrome with its associated risk
for CVD.
There have been several dual PPARa/c agonists (Chart 1) in
clinical development but most programs have been terminated
due to adverse events such as congestive heart failure in case of
muraglitazar and renal toxicity in case of tesaglitazar.8 Also the
development of aleglitazar has been stopped recently due to side
effects and lack of efficacy in an outcome study. However saroglit-
Scheme 1. Synthesis of pirinixic acid derivatives. Reagents and conditions:
(a) 2-mercaptopyrimidine-4,6-diol (1.0 equiv), R1- -bromoethylester (1.2 equiv),
azar, a preferential PPARa and dual PPARa/c agonist, was recently
a
triethylamine (1.5 equiv), DMF, 80 °C, 24 h. (b) Thioether (1 equiv), POCl3 (18 equiv),
N,N-diethylaniline (1 equiv), 90 °C, 5 h. (c) Chlorinated pyrimidine derivatives (1 eq),
R2-NH2 (1.2 eq), N-ethyldiisopropylamine (3 equiv), THF, 75 °C, 6 h or chlorinated
pyrimidine derivatives (1 equiv), R2-NH2 (1.2 equiv), sodium carbonate (1.4 equiv),
tris(dibenzylidenaceton)dipalladium(0) (0.02 equiv), Xantphos (0.06 equiv),
toluene/H2O 1:4, 85 °C, 6 h. (d) LiOH (10 equiv), THF/H2O 5:1, 80 °C, 18 h.
approved in India.
The ligand binding pocket of PPARs is quite large (>1300 Å3) and
consists of an acceptor region for the acidic head group as well as
one proximal and two distal binding pockets as important determi-
nants for ligand binding and specificity.9,10 One of the common
ways to regulate subtype selectivity of PPAR agonists consists in
the variation of the substituent size directed to the proximal
binding pocket. Larger substituents, commonly attached to the
under reflux in THF. In case of compound 7 Buchwald–Hartwig-
amination was applied for amine coupling. Therefore the 4,
6-dichloropyrimidine-derivative, (4-aminophenyl)(phenyl)metha-
none and Xantphos were dissolved in toluene followed by the addi-
tion of sodium carbonate solution. The reaction took place under
argon atmosphere using tris(dibenzylidenacetone)dipalladium(0)
as catalyst. Finally, hydrolysis with lithium hydroxide yielded the
desired carboxylic acids.
alpha-carbon of the acidic head group, are used for design of PPAR
c
preferential ligands. The same holds true for larger acidic head
group bioisosteres, like thiazolidinediones.11,12
Pirinixic acid (PA, WY 14,643, 1) has been established as an
experimental PPAR
Previously, we designed and synthesized various derivatives of
PA and characterized them as dual PPAR
agonists.13,14 In order
a agonist exhibiting micromolar activity.
a/c
PPARs activities of all synthesized compounds were screened in
a cell-based reporter gene assay with a Gal4-chimeric receptor of
the respective PPAR subtype using the Dual-Glo Luciferase Assay
System (Promega) as described previously.17 All compounds were
evaluated by comparing the achieved maximum effect with that
to gain new insights in the structure–activity relationship and
selectivity-profile of PA derivatives we present a series of new
compounds with varied lipophilic backbone. Improving selectivity
towards PPAR
In this study we are able to improve activity at PPAR
dual PPAR agonistic PA derivatives with bias towards PPARa.
c
subtype has already been achieved in the past.15,16
a
resulting in
of the respective reference compound (pioglitazone for PPAR
GW7647 for PPAR , and L165,041 for PPARd each at 1 M).
c,
a
/c
a
l
For better understanding the activation and selectivity of PPAR
receptor subtypes we present a structure-based computational
docking study besides a site-directed mutagenesis study which
supplies experimental evidence for our proposed binding mode.
Preparation of thiobarbituric acid derivatives 2–9 is outlined in
Scheme 1 and was described previously for compounds 2–3.14
The size of the substituent in the alpha position of the acidic
group may have a great impact on PPAR subtype selectivity. Initial
investigations in our group had shown that
derivatives are dual agonists of PPAR
14,13,16 Structure–activity-
relationship (SAR) studies revealed that PPAR activity could be
enhanced by enlargement of the -alkyl chain up to a hexyl chain
a-alkyl substituted PA
a/c.
a/c
a
Starting from thiobarbituric acid and the respective a-bromoe-
(2 and 3). In this study additional sets of pirinixic acid derivatives
were synthesized varying the lipophilic backbone to N-4-phenyl-
thylester nucleophilic substitution catalyzed by triethylamine
resulted in the formationof the respective thioether. In the following
step chlorination with phosphorous oxychloride afforded the 4,
6-dichloropyrimidine derivative in quantitative yield. The
introductionofan amine residuewas achievedby a nucleophilicaro-
matic substitution in the presence of N-ethyldiisopropylamine
aminophenyl in as well as the length of the
The most potent derivative of this set was compound 6. Besides a
promising activity it has a selectivity profile towards PPAR (>10
fold). Thus compound 6 reveals high activity at PPAR with an
a-alkyl chain (Table 1).
a
a
Lamers, Christina
