Inhibition of acetylcholinesterase by a pseudozoanthoxanthin-like compound isolated from the zoanthid Parazoanthus axinellae (O. Schmidt).

An ethanolic extract from a zoanthid crust coral Parazoanthus axinellae was lethal to mice and crabs and exhibited anticholinesterase activity. The isolation of several AChE inhibitors with the aid of RP-HPLC is described. The most abundant of the inhibitors present in the P. axinellae extract was identified as pseudozoanthoxanthin or an almost identical compound which belongs to the chemically well-characterized series of tetrazacyclopentazulene natural pigments from the genera Parazoanthus, Epizoanthus, Zoanthus and Palythoa. The inhibitor has a mol. wt of 242 and acts as a competitive inhibitor with a Ki of 4 microM. The inhibitor exhibited a strong blue fluorescence. In vivo action of crude extract and the isolated inhibitor showed a typical picture of systemic acetylcholinesterase inhibition. Atropinization of experimental animals prior to injection of the inhibitor almost entirely neutralized its activity.