Structurally Minimized μ‐Conotoxin Analogues as Sodium Channel Blockers: Implications for Designing Conopeptide‐Based Therapeutics

Transforming the neuroactive toxins of cone snails into small‐size compounds poses a challenge due to the presence of multiple disulfide bridges. Herein we describe our successful efforts in minimizing the size of μ‐conotoxin while retaining its biological activity. magnified image Disulfide bridges that stabilize the native conformation of conotoxins pose a challenge in the synthesis of smaller conotoxin analogues. Herein we describe the synthesis of a minimized analogue of the analgesic μ‐conotoxin KIIIA that blocks two sodium channel subtypes, the neuronal Na V 1.2 and skeletal muscle Na V 1.4. Three disulfide‐deficient analogues of KIIIA were initially synthesized in which the native disulfide bridge formed between either C1C9, C2C15, or C4C16 was removed. Deletion of the first bridge only slightly affected the peptide's bioactivity. To further minimize this analogue, the N‐terminal residue was removed and two nonessential serine residues were replaced by a single 5‐amino‐3‐oxapentanoic acid residue. The resulting “polytide” analogue retained the ability to block sodium channels and to produce analgesia. Until now, the peptidomimetic approach applied to conotoxins has progressed only modestly at best; thus, the disulfide‐deficient analogues containing backbone spacers provide an alternative advance toward the development of conopeptide‐based therapeutics.