Design, Synthesis, Pharmacology, and In Silico Studies of (1 S,2 S,3 S)-2-(( S)-Amino(carboxy)methyl)-3-(carboxymethyl)cyclopropane-1-carboxylic Acid (LBG30300): A Picomolar Potency Subtype-Selective mGlu2 Receptor Agonist

Metabotropic glutamate (Glu) receptors (mGlu receptors) play a key role in modulating excitatory neurotransmission in the central nervous system (CNS). In this study, we report the structure-based design and pharmacological evaluation of densely functionalized, conformationally restricted glutamate analogue (1S,2S,3S)-2-((S)-amino(carboxy)methyl)-3-(carboxymethyl)cyclopropane-1-carboxylic acid (LBG30300). LBG30300 was synthesized in a stereocontrolled fashion in nine steps from a commercially available optically active epoxide. Functional characterization of all eight mGlu receptor subtypes showed that LBG30300 is a picomolar agonist at mGlu₂ with excellent selectivity over mGlu₃ and the other six mGlu receptor subtypes. Bioavailability studies on mice (IV administration) confirm CNS exposure, and an in silico study predicts a binding mode of LBG30300 which induces a flipping of Tyr144 to allow for a salt bridge interaction of the acetate group with Arg271. The Tyr144 residue now prevents Arg271 from interacting with Asp146, which is a residue of differentiation between mGlu₂ and mGlu₃ and thus could explain the observed subtype selectivity.