Positive allosteric modulators of the metabotropic glutamate receptor subtype 4 (mGluR4). Part II: Challenges in hit-to-lead

The synthesis and SAR of two mGluR4 positive allosteric modulator leads 6 and 7 is described. VU001171 ( 6) represents the most potent (EC 50 = 650 nM), efficacious (141% Glu Max) and largest fold shift (36-fold) of any mGluR4 PAM ever described. However, this work highlights the challenges in hit-to-lead for mGluR4 PAMs, with multiple confirmed HTS hits displaying little or no tractable SAR. This Letter describes the synthesis and SAR of two mGluR4 positive allosteric modulator leads, 6 and 7. VU001171 ( 6) represents the most potent (EC 50 = 650 nM), efficacious (141% Glu Max) and largest fold shift (36-fold) of any mGluR4 PAM reported to date. However, this work highlights the challenges in hit-to-lead for mGluR4 PAMs, with multiple confirmed HTS hits displaying little or no tractable SAR.