Novel-Type GABA B PAMs: Structure-Activity Relationship in Light of the Protein Structure.

Selecting a known HTS hit with the pyrazolo[1,5- a ]pyrimidine core, our project was started from CMPPE, and its optimization was driven by a ligand-based pharmacophore model developed on the basis of published GABA _B positive allosteric modulators (PAMs). Our primary goal was to improve the potency by finding new enthalpic interactions. Therefore, we included the lipophilic ligand efficiency (LLE or LipE) as an objective function in the optimization that led to a carboxylic acid derivative ( 34 ). This lead candidate offers the possibility to improve potency without drastically inflating the physicochemical properties. Although the discovery of the novel carboxyl feature was surprising, it turned out to be an important element of the GABA _B PAM pharmacophore that can be perfectly explained based on the new protein structures. Rationalizing the binding mode of 34 , we analyzed the intersubunit PAM binding site of GABA _B receptor using the publicly available experimental structures.
Competing Interests: The authors declare no competing financial interest.
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