Indazole as a Phenol Bioisostere: Structure–Affinity Relationships of GluN2B-Selective NMDA Receptor Antagonists

Abstract

Negative allosteric modulation of GluN2B subunit-containing NMDA receptors prevents overstimulation, resulting in neuroprotective effects. Since the phenol of prominent negative allosteric modulators is prone to rapid glucuronidation, its bioisosteric replacement by an indazole was envisaged. The key step in the synthesis was a Sonogashira reaction of non-protected iodoindazoles with propargylpiperidine derivatives. Modification of the alkynyl moiety allowed the introduction of several functional groups. The synthesized indazoles showed very high GluN2B affinity but limited selectivity over σ receptors. Molecular dynamics simulations revealed the same molecular interactions with the ifenprodil binding site as the analogous phenols. In two-electrode voltage-clamp experiments, enantiomeric 3-(4-benzylpiperidin-1-yl)-1-(1H-indazol-5-yl)propan-1-ols (S)-10a and (R)-10a displayed higher inhibitory activity than ifenprodil. In contrast to phenolic GluN2B antagonists, the indazoles were not conjugated with glucuronic acid. It can be concluded that the phenol of potent GluN2B antagonists can be replaced bioisosterically by an indazole, retaining the high GluN2B affinity and activity but inhibiting glucuronidation.

Evaluation of the Indazole Analogs of 5-MeO-DMT and Related Tryptamines as Serotonin Receptor 2 Agonists

“…Incorporation of the indazole motif has yielded compounds with excellent properties across a number of drug discovery programs − and is present in no less than 43 compounds undergoing clinical evaluation (as of 2021) . Additionally, indazoles are known to act as effective bioisosteres for indoles and phenols, and are often superior with respect to plasma clearance, oral bioavailability, and metabolic stability. − We were therefore also interested in examining the indazole isosteres of classical psychedelics (including 5-MeO-DMT) to ultimately (1) profile the 5-HT 2A potency and serotonin-subtype selectivity of 2- aza -5-MeO-DMT and compare our data to the known literature (with a parallel emphasis on the generation of novel analogs) and (2) understand the overall properties of an indazole series of tryptamines with respect to preclinical pharmacokinetics (PK).…”