Maitotoxin (MTX) is an extremely potent biotoxin produced by Gambierdiscus toxicus, a dinoflagellate species.

Maitotoxin activates extracellular calcium channels, leading to an increase in levels of cytosolic Ca2+ ions.

It resembles large fatty acid chains and it is notable because it is one of the largest and most complex non-protein, non-polysaccharide molecules produced by any organism.

However, Andrew Gallimore and Jonathan Spencer have questioned the structure of maitotoxin at a single ring-junction (the J–K junction), based purely on biosynthetic considerations and their general model for marine polyether biogenesis.

[11] Since 1996 the Nicolaou research group is involved in an effort to synthesise the molecule via total synthesis[13][14][15][16] although as of 2015 the project is on hold due to lack of funding.