Toxic Dopamine Metabolite DOPAL Forms an Unexpected Dicatechol Pyrrole Adduct with Lysines of α‐Synuclein

Parkinson's disease has long been known to involve the loss of dopaminergic neurons in the substantia nigra and the coincidental appearance of Lewy bodies containing oligomerized forms of α‐synuclein. The “catecholaldehyde hypothesis” posits a causal link between these two central pathologies mediated by 3,4‐dihydroxyphenylacetaldehyde (DOPAL), the most toxic dopamine metabolite. Here we determine the structure of the dominant product in reactions between DOPAL and α‐synuclein, a dicatechol pyrrole lysine adduct. This novel modification results from the addition of two DOPAL molecules to the Lys sidechain amine through their aldehyde moieties and the formation of a new carbon–carbon bond between their alkyl chains to generate a pyrrole ring. The product is detectable at low concentrations of DOPAL and its discovery should provide a valuable chemical basis for future studies of DOPAL‐induced crosslinking of α‐synuclein.