A naturally-occuring neurotoxin, called Onchidal, produced by a species of sea slug acts as an irreversible inhibitor of acetylcholinesterase. The structure of Onchidal is presented below:

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How and why does Onchidal act as an AChE inhibitor? What does the adduct of Onchidal with AChE look like? Why is the inhibition of AChE by Onchidal irreversible?


There is only scarce literature about Onchidal:(

The mechanism of the AChE blockade by Onchidal was suggested to be a novel one; it was not like the Sarin-like inactivation of the serine residue in the activation site (1). Note that alpha, beta-unsaturated aldehyde in Onchidal is potentially reactive. Onchidal has been shown to give some adducts to lysine residues in an enzyme (2).

(1) Abramson SN, Radic Z, Manker D, Faulkner DJ, Taylor P. Onchidal: a naturally occurring irreversible inhibitor of acetylcholinesterase with a novel mechanism of action. Mol Pharmacol. 1989;36(3):349-354.

(2) Cadelis MM, Copp BR. Investigation of the electrophilic reactivity of the biologically active marine sesquiterpenoid onchidal and model compounds. Beilstein J Org Chem. 2018;14:2229-2235.


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