Covalent Allosteric Probe for the Metabotropic Glutamate Receptor 2: Design, Synthesis, and Pharmacological Characterization

Covalent labeling
of G protein-coupled receptors (GPCRs) by small
molecules is a powerful approach to understand binding modes, mechanism
of action, pharmacology, and even facilitate structure elucidation.
We report the first covalent positive allosteric modulator (PAM) for
a class C GPCR, the mGlu2 receptor. Three putatively covalent
mGlu2 PAMs were designed and synthesized. Pharmacological
characterization identified 2 to bind the receptor covalently.
Computational modeling combined with receptor mutagenesis revealed
T7917.29×30 as the likely position of covalent interaction.
We show how this covalent ligand can be used to characterize the PAM
binding mode and that it is a valuable tool compound in studying receptor
function and binding kinetics. Our findings advance the understanding
of the mGlu2 PAM interaction and suggest that 2 is a valuable probe for further structural and chemical biology
approaches.