Discovery of ML326: The first sub-micromolar, selective M5 PAM.
This Letter describes the further chemical optimization of the M5 PAM MLPCN probes ML129 and ML172. A multi-dimensional iterative parallel synthesis effort quickly explored isatin replacements and a number of southern heterobiaryl variations with no improvement over ML129 and ML172. An HTS campaign identified several weak M5 PAMs (M5 EC50 >10μM) with a structurally related isatin core that possessed a southern phenethyl ether linkage. While SAR within the HTS series was very shallow and unable to be optimized, grafting the phenethyl ether linkage onto the ML129/ML172 cores led to the first sub-micromolar M5 PAM, ML326 (VU0467903), (human and rat M5 EC50s of 409nM and 500nM, respectively) with excellent mAChR selectivity (M1-M4 EC50s >30μM) and a robust 20-fold leftward shift of the ACh CRC.
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CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL GENE-Y GENE-Y GENE-Y GENE-Y GENE-N CHEMICAL GENE-N GENE-Y CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL CHEMICAL
VU0467903 ACh ML129 ML172 ML326 M5 M5 M5 M5 M5 isatin mAChR M5 ML129 ML172 isatin phenethyl ether phenethyl ether ML129 ML172 ML326