Oxopyridine Sulfamoyl Fluorides for Covalent Bond Formation at Tyrosine and Inhibition of Ral GTPase

Small molecules bearing aryl sulfonyl fluorides can react with tyrosine residues to modulate protein function.Recently, we have reported several aryl sulfonyl fluoride small molecules that react at Tyr-82 of Ral RAS GTPases.Here, we explore oxopyridine sulfamoyl fluoride as an alternative reactive group for covalent inhibition of Ral GTPases.The oxopyridine sulfamoyl fluoride compounds were markedly more stable in buffer and exhibited substantially less reactivity towards free tyrosine compared to an aryl sulfonyl fluoride analog.Two fluorosulfate analogs were highly stable in buffer and did not react with free tyrosine.Aryl sulfonyl fluoride and oxopyridine sulfamoyl fluoride compounds inhibited Ral GTPase nucleotide exchange by Rgl2 and reacted at Ral Tyr-82.A high-resolution crystal structure revealed binding to the adjacent Switch I/II pocket and further confirmed reaction at Tyr-82.The oxopyridine sulfamoyl fluoride reactive group may provide the right balance of reactivity and stability for lead generation and covalent drug development for RAS GTPases and other proteins harboring promising tyrosine residues.