Verecynarmin A, a Novel Briarane Diterpenoid Isolated from Both the Mediterranean Nudibranch Molluse Armina maculata and its Prey, the Pennatulacean Octocoral Veretillum cynomorium

The briarane diterpenoid verecynarmin A (=(−)).(8 R ,9 S ,11 R ,12a R ,4 Z ,6 Z )‐11,12‐epoxy‐8,8a,9,10,12,12a,13‐octahydro‐1,5,8a,12‐tetramethylbenzo[4,5]cyclodeca[1,2‐b]furan‐9‐yl acetate; ((−)‐1) is shown to be contained in both the Mediterranean nudibranch mollusc Armina maculata (R AFINESQUE ) and its prey, the pennatulacean octocoral Veretillum cynomorium (P ALLAS ). The structure is mainly solved by 1D‐NMR, 2D‐NMR, and NOE studies of (−)‐1. However, the relative configurations at the epoxide and angular methyl centres, as well as the preferred conformation, are established by shift‐reagent and NOE studies of diol(−)‐4 obtained by epoxide‐ring opening of (−)‐1 with LiA1H 4 . The absolute configuration is established via deacetylation of (−)01 followed by Horeau's esterification.