Design, Synthesis, Pharmacology, and In Silico Studies of (1S,2S,3S)-2-((S)-Amino(carboxy)methyl)-3-(c arboxymethyl)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 mGlu(2) with excellent selectivity over mGlu(3) 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 mGlu(2 )and mGlu(3) and thus could explain the observed subtype selectivity.