Design and synthesis of potent and selective P2X3 receptor antagonists derived from PPADS as potential pain modulators

• Published in: European journal of medicinal chemistry Vol. 70; pp. 811 - 830
• Main Authors: Cho, Joong-Heui, Jung, Kwan-Young, Jung, Younghwan, Kim, Min Hye, Ko, Hyojin, Park, Chul-Seung, Kim, Yong-Chul
• Format: Journal Article
• Language: English
• Published: France Elsevier Masson SAS 2013
• Subjects: Animals; Antagonists; Dose-Response Relationship, Drug; Drug Design; Humans; Molecular Structure; Oocytes - drug effects; Oocytes - metabolism; P2X3 receptor; Pain; Pain - drug therapy; Pain - metabolism; PPADS; Pyridoxal Phosphate - analogs & derivatives; Pyridoxal Phosphate - chemical synthesis; Pyridoxal Phosphate - chemistry; Pyridoxal Phosphate - pharmacology; Receptors, Purinergic P2X3 - metabolism; Structure-Activity Relationship; Structure-activity relationships; Two-electrode voltage clamp; Xenopus; Two-electrode voltage clamp; Antagonists; Pain; PPADS; Structure-activity relationships; P2X3 receptor; P2X receptor
• ISSN: 0223-5234; 1768-3254
• DOI: 10.1016/j.ejmech.2013.10.026

Pyridoxalphosphate-6-azophenyl-2′,4′-disulfonate (7a, PPADS), a nonselective P2X receptor antagonist, was extensively modified to develop more stable, potent, and selective P2X3 receptor antagonists as potential antinociceptive agents. Based on the results of our previous report, all strong anionic groups in PPADS including phosphate and sulfonate groups were changed to carboxylic acids or deleted. The unstable azo (–NN–) linkage of 7a was transformed to more stable carbon-carbon, ether or amide linkages through the synthesis of the 5-hydroxyl-pyridine moieties with substituents at 2 position via a Diels-Alder reaction. This resulted in the retention of antagonistic activity (IC50 = 400 ∼ 700 nM) at the hP2X3 receptor in the two-electrode voltage clamp (TEVC) assay system on the Xenopus oocytes. Introduction of bulky aromatic groups at the carbon linker, as in compounds 13h–n, dramatically improved the selectivity profiles of hP2X3 when compared with mP2X1 and hP2X7 receptors. Among the substituents tested at the 2-position, the m-phenoxybenzyl group showed optimum selectivity and potency at the hP2X3 receptor. In searching for effective substituents at the 4- and 3-positions, we found that compound 36j, with 4-carboxaldehyde, 3-propenoic acid and 2-(m-phenoxy)benzyl groups, was the most potent and selective hP2X3 receptor antagonist with an IC50 of 60 nM at hP2X3 and marginal antagonistic activities of 10 μM at mP2X1 and hP2X7. Furthermore, using an ex-vivo assay system, we found that compound 36j potently inhibited pain signaling in the rat dorsal horn with 20 μM 36j displaying 65% inhibition while 20 μM pregabalin, a clinically available drug, showed only 31% inhibition. [Display omitted] •Carboxypyridine derivatives of PPADS were developed as P2X3 receptor antagonists.•We replaced unstable azo (–NN–) linker in 7a–c with stable carbon–carbon linkers.•Compound 36j was the most potent and selective hP2X3 receptor antagonist (IC50 = 60 nM).•Compound 36j potently inhibited pain signaling in rat dorsal horn.