Structure-activity relationship study of β-oxidation resistant indole-based 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2017.08.034

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is formed from 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by the 5-lipoxygenase (5-LO) pathway under conditions associated with oxidative stress. 5-Oxo-ETE is an important pro-inflammatory mediator, which stimulates the migration of eosinophils via a selective G-protein coupled receptor, known as the OXE receptor (OXE-R). Previously, we designed and synthesized structural mimics of 5-oxo-ETE such as 1 using an indole scaffold. In the present work, we added various substituents at C-3 of this moiety to block potential β-oxidation of the 5-oxo-valerate side chain, and investigated the structure-activity relationships of the resulting novel β-oxidation-resistant antagonists. Cyclopropyl and cyclobutyl substituents were well tolerated in this position, but were less potent as the highly active 3S-methyl compound. It seems likely that 3-alkyl substituents can affect the conformation of the 5-oxovalerate side chain containing the critical keto and carboxyl groups, thereby affecting interaction with the OXE-receptor.

Full text of DOI:10.1016/j.bmcl.2017.08.034

Accepted Manuscript
Structure-activity relationship study of β-oxidation resistant indole-based 5-
oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) receptor antagonists
Qiuji Ye, Shishir Chourey, Rui Wang, Chintam Nagendra Reddy, Sylvie Gravel,
William S. Powell, Joshua Rokach
PII:
S0960-894X(17)30836-3
DOI:
http://dx.doi.org/10.1016/j.bmcl.2017.08.034
BMCL 25228
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 July 2017
15 August 2017
16 August 2017
Please cite this article as: Ye, Q., Chourey, S., Wang, R., Nagendra Reddy, C., Gravel, S., Powell, W.S., Rokach,
J., Structure-activity relationship study of β-oxidation resistant indole-based 5-oxo-6,8,11,14-eicosatetraenoic acid
(5-oxo-ETE) receptor antagonists, Bioorganic & Medicinal Chemistry Letters (2017), doi: http://dx.doi.org/
10.1016/j.bmcl.2017.08.034
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Graphical Abstract
Structure-Activity Relationship Study of β-
oxidation Resistant Indole-Based 5-Oxo-6, 8,
11, 14-Eicosatetraenoic Acid (5-oxo-ETE)
Receptor Antagonists
Leave this area blank for abstract info.
Qiuji Yea, Shishir Choureya, Rui Wanga, Chintam Nagendra Reddya, Sylvie Gravelb, William S. Powellb, Joshua
Rokacha
aClaude Pepper Institute and Department of Chemistry, Florida Institute of Technology, 150 West University
Boulevard, Melbourne, FL 32901, USA
bMeakins-Christie Laboratories, Centre for Translational Biology, McGill University Hospital Centre Research
Institute, 1001 Decarie Blvd, Montreal QC H4A 3J1, Canada
Keywords: 5-oxo-ETE, eosinophil, structure-activity relationship, antagonist, asthma
1

Bioorganic & Medicinal Chemistry Letters
jo u r n a l h o m e p a g e : w w w . e ls e v i e r . c o m
Structure-activity relationship study of β-oxidation resistant indole-based 5-oxo-
6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) receptor antagonists
Qiuji Yea, Shishir Choureya, Rui Wanga, Chintam Nagendra Reddya, Sylvie Gravelb, William S. Powellb,
Joshua Rokach*a
a Claude Pepper Institute and Department of Chemistry, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA
b Meakins-Christie Laboratories, Centre for Translational Biology, McGill University Hospital Centre Research Institute, 1001 Decarie Blvd, Montreal QC H4A
3J1, Canada
* Corresponding author. Tel: 321-674-8578. Fax: 321-674-7743. E-mail: jrokach@fit.edu.
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is formed from 5S-hydroxy-6,8,11,14-
eicosatetraenoic acid (5-HETE) by the 5-lipoxygenase (5-LO) pathway under conditions
associated with oxidative stress. 5-Oxo-ETE is an important pro-inflammatory mediator, which
stimulates the migration of eosinophils via a selective G-protein coupled receptor, known as the
OXE receptor (OXE-R). Previously, we designed and synthesized structural mimics of 5-oxo-
ETE such as 1 using an indole scaffold. In the present work, we added various substituents at C-
3 of this moiety to block potential β-oxidation of the 5-oxo-valerate side chain, and investigated
the structure-activity relationships of the resulting novel β-oxidation-resistant antagonists.
Cyclopropyl and cyclobutyl substituents were well tolerated in this position, but were less potent
as the highly active 3S-methyl compound. It seems likely that 3-alkyl substituents can affect the
conformation of the 5-oxovalerate side chain containing the critical keto and carboxyl groups,
thereby affecting interaction with the OXE-receptor.
Keywords:
5-Oxo-ETE
Eosinophil
Structure-activity relationship
Antagonist
Asthma
2009 Elsevier Ltd. All rights reserved.
Arachidonic acid (AA, 2) is an ω-6 polyunsaturated fatty acid
that is a key precursor of a large number of biologically active
metabolites formed by different oxygenation pathways, one of
the most important of which is the 5-lipoxygenase (5-LO)
pathway.1-2 5-LO converts AA (2) in the presence of 5-LO
activating protein (FLAP) to 5S-hydroperoxy6,8,11,14-
eicosatetranoic acid (5S-HpETE, 3) that is further metabolized to
5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5S-HETE, 4) and
leukotrienes (LTs), Figure 1. In the presence of nicotinamide
adenine dinucleotide phosphate (NADP+), 5-HETE (4) is
oxidized by the enzyme 5-hydroxyeicosanoid dehydrogenase (5-
HEDH) to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE, 5),
which stimulates a variety of responses in human eosinophils and
neutrophils.2 Notably, 5-oxo-ETE (5) is the most potent
chemoattractant for human eosinophils among lipid mediators.3
The actions of 5-oxo-ETE are regulated by a selective Gi protein-
coupled receptor known as the OXE receptor (OXE-R), which is
most highly expressed in eosinophils compared to other cell
types. Because of these effects, activation of the OXE-R by 5-
oxo-ETE could be a key event in the progression of eosinophilic
diseases such as asthma.2-3 Unlike cysteinyl leukotriene receptor
(CysLT1) antagonists, such as Singulair (6, Figure 1), at present
there is no drug targeting the OXE receptor. For this reason, we
embarked on a search for selective OXE-R antagonists that could
block the potent proinflammatory effects of 5-oxo-ETE and
thereby be useful therapeutic agents in eosinophilic diseases such
as asthma. To this end, we designed 5-oxo-ETE receptor
antagonists based on the structural mimics of 5-oxo-ETE (Figure
2).5-6
2

Figure 1. Biochemical formation of eicosanoids by the 5-lipoxygenase (5-LO) pathway. The development of OXE receptor antagonist can stop eosinophil-
induced inflammation.
Figure 2. The design of indole-based 5-oxo-ETE receptor antagonists as structural mimics of 5-oxo-ETE. Regions required for activation of the OXE-R are
highlighted in blue.
To design OXE receptor antagonists, we first identified the
essential structural elements of 5-oxo-ETE (5) required for the
activation of the OXE-R. Structure-activity relationship (SAR)
studies revealed that the C1-carboxyl group, the 5-keto group
coupled to an adjacent conjugated system, and the hydrophobic
region at the ω-end of the molecule were all required for
biological activity (5, Figure 2).4 Based on these results, we
replaced the tetraene conjugated system of 5-oxo-ETE with an
aromatic system such as naphthalene, benzofuran, and indole, to
which we attached the carboxyl end and the alkyl (ω) end of 5-
oxo-ETE as two separate groups. Among these aromatic
scaffolds, indole (7, Figure 2) gave the most promising results.5
Using our Ca++ mobilization assay we screened a series of
indoles containing 5-oxovalerate and hexyl groups in different
positions and found that an indole containing a hexyl group in the
2-position and a 5-oxovalerate group in the 3-position was the
most potent. Further modification of this compound by the
addition of a chloro group in the 5-position resulted in a 4-fold
increase in antagonist potency and led to the lead compound 1,
which has an IC50 of 566 nM in inhibiting 5-oxo-ETE-induced
Ca++ mobilization in neutrophils.6
antagonist activities. Both 9 and 10 showed substantial decreases
in potency of seven and fourteen folds, respectively, compared to
our lead compound 1 (Figure 3B). We then introduced the
dimethyl function in the C-3 position of the 5-oxovalerate side
chain (11, Figure 3B), and found that this compound is more
potent than its regioisomers 9 and 10 (Figure 3B-C), with an IC50
only about 2-fold higher than compound 1. These results suggest
that introduction of an alkyl substituent is much better tolerated
in the 3-position of the acyl side chain than at either the 2- or 4-
positions, presumably because it is further from the keto and
carboxyl groups, both of which are critical for interaction with
the OXE-R.2 We therefore focused on the 3-position of the acyl
side chain for the addition various substituents to block β-
oxidation.
Design of structural modifications at the C-3 position of the 5-
oxovalerate side chain. We modified the C-3 position of the 5-
oxovalerate side chain by three different types of substitutions:
alkyl (Table 2), ether linkage (15, Scheme 5), and phenyl linkage
(16, and 17, Scheme 4). In the first type of modification, we
replaced the dimethyl group of 11 with different alkyl groups
(12-14, Table 2) having different Van der Waals volumes, which
can provide useful SAR information on the stereo interactions
between the antagonist and the OXE-R. For example, the
cyclopropyl group (13, Table 2), which has been applied in the
successful development of Singulair (6, Figure 1)10, contains a
unique bond angle and has a smaller Van der Waals volume (40.9
Å3) than the dimethyl group (11, 54.8 Å3). A cyclobutyl group
(14, 65.3 Å3), which can have interconvertible conformations11
(Table 2) that may interact differently with the OXE-R, was also
incorporated. Finally, introduction of a monomethyl group (12,
Table 2), which creates a chiral center in the molecule, provided
an analog with a smaller Van der Waals volume (30.3 Å3).
Because the 5-oxovalery side chain of the lead compound 1
can potentially undergo β-oxidation,7-8 we decided to modify the
carboxyl side chain of 1, to block this metabolism. To
accomplish this, we introduced various substituents at the C-2
and C-3 positions of 1 (such as 9, and 11 respectively, Figure 3).
In this paper, the syntheses and systematic SAR of these novel
indole derivatives as OXE receptor antagonists are reported.
Introduction of a dimethyl group at different positions of the
lead compound (1). In the development of a potent and specific
leukotriene biosynthesis inhibitor, MK-886 (8, Figure 3A), a
dimethyl group was incorporated in an attempt to prevent β-
oxidation of the propionic acid side chain (Figure 3A).9 We first
substituted a dimethyl group at C-2 position of the lead
compound 1 and prepared 9 (Figure 3B). In the preparation of 9,
a small amount of the 4,4-dimethyl substituted compound 10 was
generated as a side product (Scheme 3). We separated the two
isomers by column chromatography and measured their
In the second type of modification, an ether linkage was
introduced, which altered the bond angle at C-3 of the 5-
oxovalerate side chain (15, Scheme 5). In the third type of
modification, the three methylene groups of the 5-oxovalerate
side chain were replaced by a phenyl ring (16, and 17, Scheme
4), which increases rigidity of the molecule.
3

9
10
11
1
Figure 3. Panel A shows the structure of MK-886 (8), a potent leukotriene biosynthesis inhibitor. Panel B shows the structures of the dimethylated compounds
(9-11). Panel C shows the concentration-response curves for the indole compounds (1 and 9-11).
Scheme 2. An effective method to prepare the key intermediate 25. Reagents and conditions: (a) NaH, MeI, DMF, 0 °C – rt, 3 h, 98%; (b) LiAlH4, THF, -20 °C –
rt, 6 h, 98%; (c) MnO2, MeCN, rt, 12h, 97%; (d) 23, LiHMDS, THF, -78 °C – rt, 3 h, 88%; (e) H2, 10% Pd/C, EtOH, rt, 2 h, 94%.
Synthesis of the indole key intermediate (25). For the efficient
synthesis of the indole derivatives (9-17), the preparation of the
key intermediate 25 (Scheme 2) in a large quantity was required.
We developed a new cost-effective procedure and improved the
over-all yield of this key intermediate (25) from 45%6 to 75%
(Scheme 2). We began the synthesis of 25 from commercially
available 5-chloro-1H-indole-2-carboxylic acid ethyl ester 18
(Scheme 2). Accordingly, compound 18 was first N-methylated
using NaH and CH3I. During the aqueous work-up of this
reaction, a small amount (5-10%) of the ester 19 was hydrolyzed
to the carboxylic acid 20. Both the ester 19 and the carboxylic
acid 20 were simultaneously reduced by LiAlH4 to obtain the
alcohol 21, which was further oxidized to the aldehyde 22 by
MnO2. Further, a Wittig reaction was carried out using the
commercially available phosphonium salt 23 to give the olefin
24. Since the nitrogen in the indole aldehyde 22 was methylated,
there was no trans/cis selectivity in the formation of the olefin
24.12 The olefin 24, which contained a pair of trans and cis
isomers, was hydrogenated to get the desired key intermediate
25. It is also worth noting that we observed a small extent (~2%)
of dechlorination in the hydrogenation reaction (Step e, Scheme
2), resulting a dechlorination product that was subsequently
removed by silica-gel column chromatography.
under the aqueous basic conditions produced the final product 16.
In the same fashion, we synthesized the para-phenyl-linked
compound 17.
Scheme 3. Preparation of the 2,2-dimethyl derivative 9, and the in-situ
generation of the 4,4-dimethyl derivative 10. Reagents and conditions: (a) 26,
Me2AlCl, CH2Cl2, 0 °C – rt, 4 h, 67% (calculated for 9).
For the synthesis of the C-3 substituted derivatives, we
applied a series of 5-oxovalerate synthons (33-36, 46, and 47)
possessing the alkyl substitutions and the ether function at the C-
3 position (Scheme 5). Scheme 5A shows the synthesis of
Compound 1, 11, 12, and 15. Friedel-Crafts acylation of 25 with
one of the commercially available anhydrides 33, 34, 35, or 36
afforded 1, 12, 11, and 15, respectively. Scheme 5B shows the
syntheses of Compounds 13 and 14. Because of the commercial
unavailability of the cyclobutyl and cyclopropyl anhydrides (46
and 47, respectively), we developed a synthetic route to prepare
these compounds. For the synthesis of 46, the malonic acid
derivative 37 was reduced with LiAlH4 to furnish the diol 38 in
90% yield. Iodination of the diol 38 using PPh3 and I2 yielded the
bis-iodide compound 40, which was subsequently converted to
the dicyano compound 42 using KCN. Hydrolysis of 42 under
basic conditions13 furnished 44, which was cyclized to 3-
cyclobutyl glutaric anhydride (46) using acetic anhydride. Friedel
Crafts acylation of 25 with 46 afforded the desired target
compound 14 in good yield. We synthesized the cyclopropyl
derivative 13 using the same method.
Synthesis of indole antagonists. After the preparation of the
key intermediate 25, the 2,2-dimethylated compound 9 was
prepared by using the anhydride 26 (Scheme 3). As expected, the
Friedel Crafts acylation took place preferentially at the less
sterically hindered side of the anhydride 26 and generated 9 as
the main product, along with a smaller amount (20%) of the 4,4-
dimethylated compound 10, which were partially separated by
silica-gel column chromatography, and were further purified by
HPLC.
We also synthesized the meta- and para- phenyl-linked
compounds 16 and 17 as shown in Scheme 4. Accordingly, the
isophthalic acid derivative 27 was reacted with oxalyl chloride to
give the acid chloride 29, which was then directly coupled with
25 via Friedel Crafts acylation to yield 31. Hydrolysis of 31
4

Scheme 4. Synthesis of the Compounds 16, and 17. Reagents and conditions: (a) oxalyl chloride, DMF (5%), CH2Cl2, 0 °C – rt, 1 h, 90%; (b) 25, Me2AlCl,
CH2Cl2, 0 °C – rt, 4 h, 26%; (c) LiOH·H2O, H2O, THF, rt, 3.5 h, 75%.
Scheme 5. Synthesis of the Compounds 1, and 11-15. Reagents and conditions: (a) 25, Me2AlCl, CH2Cl2, 0 °C – rt, 4 h; (b) LiAlH4, THF, -20 °C – rt, 6 h, 95%;
(c) Imidazole, PPh3, I2, CH2Cl2, 0 °C – rt, 16 h, 89%; (d) KCN, DMSO, rt, 24 h, 95%; (e) NaOH, H2O, MeOH, rt – reflux, 18 h, 93%; (f) Ac2O, reflux, 18 h,
96%; (g) 25, Me2AlCl, CH2Cl2, 0 °C – rt, 4 h, 86% (yield is calculated for the synthesis of 14).
Figure 4. Preparation of the R-synthon (49) by using pig liver esterase (PLE), and the chiral inversion of the R chiral synthon 49 into the S chiral synthon 51.13
Since the monomethyl substituted compound 12 possess a
chiral center at C-3 of the 5-oxovalerate substituent, we prepared
its R and S enantiomers by the method we reported previously
(Figure 4, and Scheme 7).14 The R chiral synthon 49 was
prepared from the symmetrical starting material 48 by an
enzymatic method with pig liver esterase (PLE), and the S chiral
synthon 51 was converted from 49 through a chiral inversion
strategy without any chiral dilution (Figure 4). Further reactions
of the chiral synthons 49 and 51 yielded the desired R-isomer 52
noted above, the presence of a dimethyl group at this position
(11, Entry 4) lowered the potency by about 2-fold. In contrast,
cyclopropyl (13) or cyclobutyl (14) groups in the 3-position had
absolutely no effect on antagonist potency (Table 1, entries 5 and
6; Figure 5). It is interesting that the cyclobutyl-substituted
compound 14 (65 Å3) is more potent than the 3,3-dimethyl
compound 11 (55 Å3) and equipotent with the corresponding
cyclopropyl derivative 13 (41 Å3) in view of its greater Van der
Waals volume. Finally, substitution of a methyl group at the C-3
position enhanced potency by 35 times (12, Entry 7) compared to
the non-substituted compound 1.
and S-isomer 53 respectively. We also developed
a
stereoselective method for the synthesis of the enantiomer of 49.
In this method, the S-methyl center at C-3 was generated by the
CuBr/(S)-Tol-BINAP catalyzed asymmetric conjugate addition
of MeMgBr to an α,β-unsaturated ester.15
Antagonist activities of the indole derivatives. The antagonist
potencies of all of the derivatives of the lead compound 1 were
compared by assessing their abilities to block 5-oxo-ETE-
induced Ca++ mobilization in human neutrophils (Table 1). The
insertion of an oxygen atom in the side chain increased the
polarity of the compound and reduced the potency by almost 10
times (15, Entry 1). Introduction of an aromatic system in the 5-
oxo-valerate side chain (16, and 17) reduced the potency by over
two-fold compared to the lead compound 1 (Entries 2 and 3,
Table 1).
13
14
1
We then evaluated the effects of various alkyl substituents at
the C-3 position of the 5-oxovalerate side chain (Entries 4-7). As
Figure 5. Concentration-response curves for Compounds 1, 13, and 14.
5

To better understand the SAR results for the alkyl substituted
derivatives (Compounds 11-14), we focused on the steric effect
of the alkyl substitutions at C-3 of the 5-oxovalerate chain (Table
2). By comparing the Van der Waals volume of the selected
atoms, it appears that the derivatives with smaller steric effect at
the C-3 position tends to be more active. We expected that the
cyclobutyl compound 14 would be less potent than the dimethyl
compound 11 and the cyclopropyl compound 13 because of its
greater Van der Waals volume. This may be because of the
flexibility of the cyclobutane ring, resulting in two favored
conformations, one of which may interact more strongly with the
OXE-R. Furthermore, the Van der Waals volume of the two
methylene groups of the cyclobutane ring that are closest to the
side chain (i.e. C-1 and C-3) (14, as highlighted in Table 2) is
smaller than that of the dimethyl group (11, Table 2), which
would be consistent with an effect of the volume of the
substituent.
In contrast to the substitution effect on the 5-oxovalerate side
chain, there was relatively little effect of adding alkyl groups to
the hexyl side chain of 12 (Figure 7).16
Table 1. Activity of the indole compounds on OXE receptor in Ca++ mobilization assay.
Lead Compound, 1
IC50= 566 ± 92 nM(n=5)
Entry
Stucture
IC50 (nM) n Entry
Stucture
IC50 (nM) n Entry
Stucture
IC50 (nM) n
16 ± 3 14
1
5500
3
4
5
6
1330 ± 100 4
720 ± 130 3
580 ± 110 4
7
8
9
15
17
16
11
14
13
12
52
53
2
3
1360 ± 130 7
1120 ± 200 7
2700
4
4
6 ± 0.1
Table 2. Activity and Van der Waals volume of the selected atoms at the C-3 position of the 5-oxovalerate chain. The result
suggests that derivatives with smaller steric effect at the C-3 position tend to be more active.
Introduction of an alkyl
group at C-3 position
Structure of the Indole Scaffold
Dimethyl (11)
54.8 Å3
Cyclobutyl (14)
Cyclobutyl (14)*
Cyclopropyl (13) Monomethyl (12)
Van der Waals Volume
of The Selected Atoms
65.3 Å3
48.9 Å3
40.9 Å3
30.3 Å3
IC50 Value (μM)
1.33
0.72
0.58
0.02
*The total volume of the cyclobutyl substituent (14) is 65.3 Å3. The volume in the present column contains only 1- and 3- methylene
groups of the cyclobutyl group.
6

A
B
S-methyl
derivative
R-methyl
derivative
Hypothetical OXE Receptor
Hypothetical OXE Receptor
Figure 6. A hypothetical molecular model of 53, and 52 with the OXE receptor. Due to the conformation of the S-methyl group, which is parallel to the plane of
the molecule, 53 has less interference with the receptor (Panel A). The R-methyl group in 52 is extended out of the plane of the molecule, and could exert steric
hindrance at the binding region of the OXE receptor.
Over 30 folds enhancement of the activity on a racemic
methyl substitution (12, Entry 8, Table 1) prompted us to study
the activity of individual enantiomer. We tested the activity of
each individual enantiomer of 12, and found that the S-isomer
(53, Entry 9, Table 1) is 300 times more potent than the R-isomer
(52, Entry 8).14 This dramatic difference between the S-
enantiomer 53 and R-enantiomer 52 could be explained based on
a hypothetical model of the interaction of these antagonists with
the OXE receptor as depicted in Figure 6. It shows that the S-
enantiomer 53 fits better on the binding domain of the receptor
(Figure 6A), while the methyl group of the R-enantiomer 52
exerts steric hindrance with the receptor (Figure 6B). Notably,
the orientation of the methyl groups has a profound effect on the
activity of these antagonist, which is also evident from the in
vitro results that the dimethyl compound 4 has the IC50 value
(1330 nM, Table 1) as a midway between the IC50 values of the
S-enantiomer 53 and R-enantiomer 52 (6 nM, and 2700 nM,
respectively, Table 1).
group. Replacement of the CH2 group at C-3 of the 5-oxo-
valerate side chain by an aromatic system (16, and 17) or an ether
linkage (15) reduced antagonist activity significantly. In contrast,
the presence of cyclopropyl (13) or cyclobutyl (14) substituents
in this position did not diminish potency, in spite of their bulk.
None of the compounds tested in the current study were as potent
as the 3-S-methyl compound 53. Thus, substituents in the 3-
position of this series of OXE-R antagonists are well tolerated,
and, in the case of the 3S-methyl group, can markedly increase
potency. It would seem likely that 3-alkyl substituents, in
particular the 3S-methyl group, can affect the conformation of the
5-oxovalerate side chain, probably altering the relative positions
of the keto and carboxyl groups, which are key receptor binding
components of 5-oxo-ETE. These findings are useful for the
future design and development of 5-oxo-ETE receptor
antagonists, which can be potential therapeutic agents for the
treatment eosinophilic diseases such as allergic asthma.
We have examined the effect of alkyl substitutions at the
hexyl side chain in compound 12 (Figure 7). The antagonist
potency of the branched side chain compound 5416 is about four
times less than 12, whereas the second branched compound 5516
and the extended side chain compound 56 have almost the same
activity as 12. These results show that the alkyl substituted
compounds (55-56, Figure 7) are as good as the linear hexyl
compound 12 in blocking the effects of 5-oxo-ETE.
Modifications at the alkyl end of the molecule will be conducted
in our further studies.
In summary, the structure-activity relationship study of β-
oxidation-resistant novel indole-based OXE-R antagonists is
described. Since the OXE-R has not yet been crystalized,
different computational models of the OXE-R were reported by
two groups independently.17-18 In our manuscript, we studied the
SAR of the indole-based antagonists by analyzing the Van der
Waals volume of the substituents at 3-position (Table 2). Based
on the structure of the lead compound 1, modifications were
introduced to prevent the 5-oxovalerate side chain from being
metabolized through the β-oxidation pathway. Because 2,2-
dimethyl- (9) and 4,4-dimethyl- (10) substituted compounds were
less potent than the 3,3-dimethyl-substituted compound (11)
(Figure 3) we focused on the 3-position of the 5-oxovalerate
Figure 7. Structures and IC50 values of 12, the branched derivatives (54-55),
and the extended side chain compound 56.
Acknowledgments
This work was supported by the American Asthma
Foundation (J. R.; Award Number 12-0049), and the Canadian
Institutes of Health Research (W. S. P.; MOP-6254 and PP2-
7

Tzardi, M.; Notas, G.; Castanas, E.; Kampa, M. Scientific reports
2017, 7, 44418.
133388). The Meakins-Christie Laboratories-MUHC-RI are
supported in part by a Center grant from Le Fond de la
Recherche en Santé du Québec as well as by the J. T. Costello
Memorial Research Fund. J. R. wishes to acknowledge the
National Science Foundation AMX-360 (Grant CHE-90-13145)
and Bruker 400 MHz (Grant CHE-03-42251) NMR instrument.
Abbreviations
AA, arachidonic acid; 5-HETE, 5-hydroxy-6E,8Z,11Z,14Z-
eicosatetraenoic acid; 5-oxo-ETE, 5-oxo-6E,8Z,11Z,14Z-
eicosatetraenoic
acid;
5-HEDH,
5-hydroxyeicosanoid
dehydrogenase; 5-HpETE, 5-hydroperoxyeicosatetraenoic acid;
LT, leukotriene; NADP+, nicotinamide adenine dinucleotide
phosphate; HPLC, high-performance liquid chromatography;
TLC, thin layer chromatography; Hex, hexane; EtOAc, ethyl
acetate; rt, room temperature.
Supporting Information
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.bmcl.
References and notes
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2.
3.
Powell, W. S.; Rokach, J. Prog Lipid Res 2013, 52 (4), 651-665.
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