Secondary metabolome and its defensive role in the aeolidoidean <i>Phyllodesmium longicirrum</i>, (Gastropoda, Heterobranchia, Nudibranchia)

Abstract

<i>Phyllodesmium longicirrum</i> is the largest aeolidoidean species known to date, and extremely rich in terpenoid chemistry. Herein we report the isolation of a total of 19 secondary metabolites from a single specimen of this species, i.e., steroids <b>1-4</b>, cembranoid diterpenes <b>5-13</b>, complex biscembranoids <b>14</b> and <b>15</b>, and the chatancin-type diterpenes <b>16-19</b>. These compounds resemble those from soft corals of the genus <i>Sarcophyton</i>, of which to date, however, only <i>S. trocheliophorum</i> is described as a food source for <i>P. longicirrum</i>. Fish feeding deterrent activity was determined using the tropical puffer fish <i>Canthigaster solandri</i>, and showed activity for (2<i>S</i>)-isosarcophytoxide (<b>10</b>), cembranoid bisepoxide <b>12</b> and 4-oxochatancin (<b>16</b>). Determining the metabolome of <i>P. longicirrum</i> and its bioactivity, makes it evident that this seemingly vulnerable soft bodied animal is well protected from fish by its chemical arsenal.