Do GluN2B subunit containing NMDA receptors tolerate a fluorine atom in the phenylalkyl side chain?

The influence of an F-atom in the side chain of benzo[7]annulen-7-amines on the affinity towards GluN2B subunit containing NMDA receptors and the selectivity over related receptors was investigated. The synthesis of 5a and 5b was performed by reductive amination of the ketone 6 with primary alkanamines 14a and 14b bearing an F-atom in β-position. The GluN2B affinities of non-fluorinated and fluorinated ligands 4 and 5 are almost identical. The low impact of the F-atom on GluN2B affinity was unexpected, as it influences several chemical and physicochemical properties of the ligands. However, introduction of the F-atom led to reduced selectivity over σ receptors. Whereas 5a and 5b display still a 2-3-fold preference for GluN2B over σ₁ receptors, they show almost the same affinity to GluN2B and σ₂ receptors.