Methylation of zoanthoxanthins

The methylation of parazoanthoxanthin D (1) and zoantboxanthin (2), two natural tetrazacyclopentazulene pigments from Parazoanthus axinellae, has been examined under various conditions. As a rule, methylation in neutral or acidic conditions proceeds preferentially at N-1, while in liquid ammonia zoanthoxanthins are attacked by methyl iodide exclusively at the amino group at C-2. In addition to providing information on zoanthoxanthin tautomerism, the availability of various synthetic derivatives (3–10) led to the identification of the methyl derivatives 4 and 9 in Parazoanthus axinellae, and of 5 in Epizoanthus arenaceus, another zoanthid commonly found in the Bay of Naples.