Optimization and characterization of triazole urea inhibitors for abhydrolase domain containing protein 6 (ABHD6)

Endocannabinoids (ECs) are a unique group of lipids that function as chemical messengers in the nervous system. The two principle ECs thus far identified in mammals are -arachidonoyl-ethanolamine (anandamide) and 2-arachidonoyl-glycerol (2-AG). These compounds have been implicated in various physiological and pathological functions including appetite, pain, sensation, memory, and addiction. Because ECs are synthesized and released on demand and then rapidly degraded to terminate signaling, the metabolic pathways that govern EC turnover directly influence the magnitude and duration of neuronal signaling events. Three of the key enzymes responsible for 2-AG hydrolysis (and thus inactivation) are monoacylglycerol lipase (MAGL), abhydrolase domain containing proteins 6 (ABHD6), and ABHD12. In an effort to develop more potent, active ABHD6 inhibitors, both to serve as control probes for the recently developed dual DAGL-β/ABHD6 inhibitor ML294 and for biological investigation of ABHD6 in its own right, we initiated a competitive activity-based protein profiling (ABPP)-guided medicinal chemistry campaign to identify and optimize ABHD6 inhibitors based on the triazole urea scaffold. This campaign, made possible by previous MLPCN probe development efforts for LYPLA1/2 (ML211), PAFAH2 (ML225), ABHD11 (ML226), and DAGL-β (ML294) yielded the medchem-optimized probes ML295 (SID 125269138) and ML296 (SID 125269096). These compounds exhibit low nM potency and , high selectivity among the serine hydrolase superfamily, and strong inhibitory activity . The key distinguishing feature of ML295 compared to ML296 is that the former compound is brain-penetrant, while the latter compound is peripherally-restricted in mice. These compounds, together, thus provide key pharmacological tools for dissecting the functions of ABHD6 in central vrs peripheral tissues. These successful probe development efforts further confirm the privileged nature of the triazole urea scaffold for potent and selective inhibition of serine hydrolase targets in living systems.