Calenzanol, the first member of a new class of sesquiterpene with a novel skeleton isolated from the red seaweed Laurencia microcladia from the Bay of Calenzana, Elba Island

The sesquiterpene calenzanol 1, the major metabolite of the red seaweed Laurencia microcladia Kützing from the Bay of Calenzana in Elba Island, possesses a previously unreported ring system, thus establishing a new class of sesquiterpene with a novel skeleton, calenzanane 2. Because of the special array of functionalities, 1 exhibits marked instability, readily rearranging to give the novel indene 3.