Coralloidin C, D, and E: Novel Eudesmane Sesquiterpenoids from the Mediterranean Alcyonacean Alcyonium coralloides

The Mediterranean alcyonacean Alcyonium (= Parerythropodium ) coralloides (Pallas, 1766) is shown to contain the novel eudesmane sesquiterpenoids coralloidin C (=(–)−(4 R ,10 S )‐eudesma‐5,7(11)‐dien‐15‐yl acetate; (–)− 4 ), coralloidin D (=(–)−(10 R *)‐eudesma‐4,7(11)‐diene‐12,13‐diyl diacetate; (–)− 7 ), and coralloidin E (=(+)−(4 R *,10 R *)‐eudesma‐5,7‐dien‐11‐ol;(+)− 8 ). The absolute configuration of (–)− 4 is derived by the exciton‐coupling method, applied to deacetylcoralloidin C p ‐anisate ((–)− 6 ). Coralloidin E((+)− 8 ), being also obtained on treatment of deacetylcoralloidin A (=(+)−(4 R *, 8 R *, 10 R *)‐eudesma‐5,7(11)‐dien‐8‐ol; (+)− 2 ) with (COCl) 2 in DMSO, is configurationally correlated to coralloidin A (=(+)−(4 R *, 8 R *, 10 R *)‐eudesma‐5,7(11)‐dien‐8‐yl acetate; (+)− 1 ). Under acidic conditions, (+)− 2 undergoes a complex rearrangement giving (+)‐(3 R *, 4 S *, 5 R *, 6 R *, 7 S *)‐arist‐10‐(1)‐en ‐3‐ol ((+)− 9 ), which is also obtained, together with (+)− 8 , on attempts to mesylate (+)− 2 .