Optimization of a Small Molecule Inhibitor for the Botulinum Neurotoxin Type A Protease
Mentor:Nicholas Salzameda, Assistant Professor Organic & Bioorganic Chemistry, California State University, Fullerton
The botulinum neurotoxin (BoNT), a zinc metalloprotease produced by the bacteria Clostridium botulinum, is the most lethal neurotoxin known to man. Currently, there are no therapeutic treatments for BoNT intoxication. The BoNT is composed of two proteins: a 100 kDa heavy chain (HC) and a 50 kDa light chain (LC) linked by a disulfide bond. The heavy chain binds to glycoprotein structures on cholinergic nerve terminals, where the light chain is detached and inserted into the cytoplasm. The light chain, a metalloprotease, cleaves synaptic proteins that are vital for proper neurotransmission. Because of its proteolytic activity, it is a target for therapeutic treatments of BoNT infection. Previously, we have identified a lead inhibitor for the BoNT protease. This lead inhibitor was studied via structure activity relationship (SAR) study to identify structural elements needed for inhibition of the BoNT LC protease. It was determined that three major elements were of importance for the lead inhibitor: a hydroxamate portion, an amino acid and a sulfonyl chloride portion containing a biphenyl ring system. Results showed that a hydroxamic acid portion is crucial for inhibitory activity of the small molecule, and that the most effective amino acid is D-isoleucine. In that study, we increased the inhibitor’s potency ten-fold, from an IC50 value of 10μM to 0.95μM. We now report our second generation SAR study on the improved inhibitor, on which we focus on the biphenyl ring system of the sulfonyl chloride portion. Based on a novel synthetic route to form sulfonyl chlorides, we plan to synthesize numerous analogs of the improved inhibitor by varying the sulfonyl group of the molecule and test their inhibitor activity for the BoNT protease.