Two Potent OXE-R Antagonists: Assignment of Stereochemistry

Abstract

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is formed by the oxidation of 5-hydroxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-HETE), which is a major metabolite of enzymatic oxidation of arachidonic acid (AA). 5-Oxo-ETE is the most potent lipid chemoattractant for human eosinophils. Its actions are mediated by the selective OXE receptor, which is therefore an attractive target in eosinophilic diseases such as allergic rhinitis and asthma. Recently, we have reported two excellent OXE receptor antagonists that have IC 50 values at low nanomolar concentrations. Each of these antagonists has a chiral center, and the isolation of the individual enantiomers by chiral high-performance liquid chromatography (HPLC) revealed that in each case one enantiomer is over 300 times more potent than the other. To unambiguously assign the stereochemistry of these enantiomers and to provide access to larger amounts of the active compounds for biological testing, we report here their total synthesis. KEYWORDS: 5-Oxo-ETE, eosinophil, OXE receptor, antagonist, enantiomeric, optical purity, chiral auxiliary A sthma is a complex disease, which is essentially characterized by a bronchoconstriction. In most cases it is composed of an early phase (or acute) and a late-phase (or inflammatory) asthma. One of the hallmarks of the disease is the accumulation of eosinophils in the early phase, which is then responsible for the late-phase. 5-Oxo-ETE is a potent eosinophil chemotactic factor 1,2 and responsible for the accumulation of eosinophils in the lungs 3 (Figure 1).It is formed from arachidonic acid (AA) by the 5-lipoxygenase (5-LO) pathway, following oxidation of 5-hydroxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-HETE) by 5-hydroxyeicosanoid dehydrogenase in the presence of NADP + (Figure 2). 4,5 After the first total synthesis of 5-oxo-ETE, 6 we have identified and investigated the activities of its metabolites on the 5-oxo-ETE receptor (OXE-R). 7 We found that a metabolite of 5-oxo-ETE formed by platelets, 5-oxo-12(S)-HETE, inhibits 5-oxo-ETE-induced Ca 2+ mobilization, though not increasing intracellular Ca 2+ concentration by itself. 8 However, this compound is not suitable for the development of an OXE-R antagonist as it is not stable under physiological conditions. Studies on a variety of 5-oxo-ETE analogues clearly showed that the carboxyl, carbonyl (including the 5-oxo group), and the alkyl regions of the molecule are essential for biological activity. 9 We therefore sought to develop synthetic OXE-R antagonists by incorporating both 5-oxo-valeryl and hexyl groups onto an indole backbone. The selection of the indole system looked more promising. We synthesized other aromatic scaffolds such as naphthalene, benzofuran, and quinoline, which turned out to be inactive. These studies culminated in the identification of two potent OXE-R antagonists (Figure 3) with IC 50 values of less than 30 nM. 10,11 Both of these compounds (5 and 6) have an asymmetric center on their acyl side chain, and it seemed likely that their activiti...

In vivo α-hydroxylation of a 2-alkylindole antagonist of the OXE receptor for the eosinophil chemoattractant 5-oxo-6,8,11,14-eicosatetraenoic acid in monkeys

“…For further studies on the pharmacokinetics and metabolism of 230 we focused on the active S-enantiomer ( S230 ), which is over 400 times more potent than the R-enantiomer ( R230 ) [8, 9]. To provide the gram-amounts of antagonist that would be required for this and subsequent in vivo studies we developed a novel procedure using the chiral reagent (S)-Tol-BINAP for the synthesis of the chiral acyl side chain of S230 [11].…”

“…Modification of this compound led to the identification of the chiral compound 230 (Fig. 1) as a potent and selective OXE receptor antagonist [8], with the antagonist activity residing almost exclusively in the S-enantiomer ( S230 ) [9]. …”

Biosynthesis, biological effects, and receptors of hydroxyeicosatetraenoic acids (HETEs) and oxoeicosatetraenoic acids (oxo-ETEs) derived from arachidonic acid

“…This compound is a racemic mixture of two enantiomers, separation of which by chiral-HPLC revealed that the biological activity resides almost exclusively in a single enantiomer. We were able to synthesize both enantiomers by chiral synthesis [175] and found the S-enantiomer (i.e. S-264 ) was the one with potent antagonist activity (Fig.…”

Metabolomics Reveals Process of Allergic Rhinitis Patients with Single- and Double-Species Mite Subcutaneous Immunotherapy

“…Although it possesses only weak biological activity itself, 5-HETE can be oxidized to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), which is a potent chemoattractant for eosinophils and neutrophils [22] and a major metabolite of enzymatic oxidation of AA. 5-oxo-ETE may be an important mediator in asthma, and an attractive target in eosinophilic diseases, such as AR and asthma [23,24]. Several lines of evidence indicate that respiratory infection and cell injury may activate the 12/15-LOX pathway in airway epithelial cells, and markedly increase their production of AA, 12-S-HETE and 15-HETE, which play a pathophysiological role in asthma [25,26].…”