2
J. Peng et al. / Bioorg. Med. Chem. Lett. xxx (2015) xxx–xxx
comparison with O-linked series, S-linked series were easy to be
Br
HO
Br
O
N
synthesized and obtained with high yields, and thus a variety of
molecules using S as linker with different bicyclic templates were
prepared. Their activities are summarized in Table 1. Shifting of the
nitrogen atom of quinazoline had dramatic effects on activity. As
seen in the table, movement of the 3-nitrogen atom of quinazoline
O
Cl
O
N
O
Br
S
OH
OH
N
N
O
1
0 gave compound 11, of which the IC50 was quite high (>10 lM).
3
1
2
However, further shifting of the nitrogen to 6-position of quinazo-
line gave 12 with an IC50 of 1932 nM.
Benzbromarone
Lesinurad (RDEA-594)
JTT-552
Figure 1. Selected URAT1 inhibitor disclosed in the literature.
A remarkable improvement was achieved by removing the
3
1
-nitrogen atom of quinazoline 10, and the resulting quinoline
3 had inhibition activity of 448.0 nM. The remaining nitrogen of
Targeting the transporter URAT1 is a straightforward and
quinoline template in 13 was critical and the activity was lost if
removed or shifted as in compounds 14 and 15.
important strategy to control serum urate level. Lesinurad was dis-
covered by Ardea Biosciences and it significantly reduced serum
uric acid in clinics.1 Herein, we describe some of our work that
has led to the identification of the clinical candidate compound 41.
8
Optimization of lead 13 and SAR exploring of quinoline series
From the data of compounds 11, 12 and 13, it was suggested
that further optimization could be performed on the left side of
quinoline 13. The 3D Pharmacophore alignment of 4 and 13 also
confirmed that the 6 and 7 position of the quinoline core could
be a direction for further modification. In addition, the size of the
cyclobutyl ring could also be explored. A set of compounds were
synthesized following Scheme 1 to optimize activity and the data
was listed in Table 2.
3
D pharmacophore-based lead generation
Due to the lack of structural information of URAT1, we decided
to use ligand-based 3D pharmacophore approach to guide the lead
finding effort. Four structurally diverse URAT1 inhibitors (4–7)
were selected from patents as the training set.1
9–22
Their structures
and published activities were shown in Figure 2. Based on prior
success,2 HipHop method was attempted which resulted in a
highest ranked model Hypo1 (Fig. 3A), containing the following
pharmacophore features, one Negative Ionizable (NI), two
Hydrophobic (HY) and one Ring Aromatic (RA). For further opti-
mization, Hypo1 was refined with known inactive compounds 8
as listed in Figure 2 using the protocol ‘Steric Refinement With
Excluded Volumes’ implemented in DiscoveryStudio.25 Based on
the result, one excluded volume was added to the Hypo1 (shown
as the gray ball in Fig. 3B). In Figure 3B, the active compounds 4
and 7 from the training set were mapped onto the final pharma-
cophore model.
3
24
Installation of the 4-substitutent of quinoline 16 was achieved
by modification of 4-chloroqunioline under several functional
group transformation steps. Displacement of the chloride of 16
using sodium sulfide gave the thiol compound 17, which was sub-
sequently alkylated with ethyl 1-bromocyclo-butane-carboxylate
under the conditions of cesium carbonate in hot DMF. Further
26
standard Suzuki coupling of the corresponding 6-bromoquinoline
8 with a variety of boronic acids provided the esters, which were
1
hydrolyzed under the basic conditions to yield the final acids 20.
As for the 6-methoxyquinoline series, removal of the methyl
group with boron tribromide released 22 with the free hydroxyl
group. Followed by alkylation under the conditions of sodium
hydride and related halide in DMF and hydrolysis of the ethyl
ester, 6-hydroxylquinoline was converted to the desired acids 23.
Initially, polar groups like nitrile, amine and hydroxyl (in 24, 25
and 26) were installed at the 6 position of quinoline 13. It turned
out that only the nitrile compound 24 had a comparable IC50 of
According to the 3D Pharmacophore Hypo1, structurally differ-
ent compounds were aligned together. Based on the alignment of 4
and 7 (Fig. 3B), we carried out the hybrid design and synthesized a
series of bicyclic compounds (Table 1). Firstly the readily available
bicyclic quinazoline was used as template, and the portion with a
carboxylic acid group attached to an aliphatic ring was linked to
the quinazoline template via O or S atom. However, both these
3
98.8 nM and activities of the other two compounds dropped sig-
two compounds 9 and 10 gave us activity of more than 10 lM. In
nificantly. But the result indicated that it did have room for further
optimization within this region. A variety of polar groups with cer-
tain flexibility (27–36) were introduced at the same position of
lead compound 13 to enhance hURAT1 activities. It was observed
that compounds 31 and 32 with methoxyl group attached to the
quinoline template via oxygen or carbon chain linker had IC50 of
206.9 nM and 197.8 nM, respectively. However, the rigid amide
CN
O
S
O
N
CF
3
OH
series 34, 35 and 36 gave very poor activities (>10 lM) against
hURAT1.
O
CN
OH
6
OH
IC50 = 80 nM
Having improved IC50 from 448.0 nM to 197.8 nM (32) with the
polar methoxymethyl group, we then focused our efforts on
the influence of non-polar groups to their activities. Compounds
5
4
O
a
IC50 < 50 nM
IC50 = 86 nM
O
O
O
3
7–44 were synthesized and typical hydrophobic groups of different
sizes were attached to the quinoline scaffold. Surprisingly, compound
9 with trifluoromethyl group showed an IC50 of 61.2 nM and even
O
N
N
O
3
Cl
Cl
higher activity against hURAT1 was achieved for 6-bromoquinoline
41 with an IC50 of 33.7 nM. The Br atom must have played an
important role in the binding with receptor and 7-bromoquinoline
compound 42 also had a decent activity of 129.8 nM.
Further tuning of the top-right moiety, displacement of
cyclobutane in 41 with cyclopentane (in 43) and cyclopropane
(in 44) showed inferior activities, and thus the cyclobutane ring
O
OH
OH
Cl
7
8
Cl
IC50 < 100 nM
IC50 > 1000 nM
Figure 2. Chemical structures of URAT1 inhibitors in the training set with their
biological activity. a IC50 value was measured in house.