Botulinum neurotoxin serotype A (BoNTA) is one of the most toxic substances known. Currently there is no antidote to BoNTA. Small molecules identified from high-throughput screening reportedly inhibit the endopeptidase - the zinc-bound, catalytic domain of BoNTA - at a drug concentration of 20 M. However, optimization of these inhibitors is hampered by challenges including the computational evaluation of the ability of a zinc ligand to compete for coordination with ...