Further insights into the oxidation chemistry of 5-hydroxytryptamine

An important product of electrochemical oxidation of 5-hydroxytryptamine (5-HT) in acid solution is the purple compound tryptamine-4,5-dione (6). However, any attempt to concentrate a solution containing 6 causes it to disappear. The most important reaction of 6 is dimerization to give another purple compound 7,7'-bi-(5-hydroxytryptamine-4-one). Dione 6 can also apparently react with 2,4'-bi-5-hydroxytryptamine to give the trimer 4-[7'-(tryptamine-4,5-dione)]-2,4''-bi-5-hydroxytryptamine. Finally, 6 and other oxidation products of 5-HT react during the concentration step to yield what appears to be a trimer or perhaps a higher oligomer. This oligomer has not been identified, but it has been shown to decompose to give, in part, the neurotoxin 5-hydroxytryptamine-4,7-dione.