Isolation from the Mediterranean Stolonifern Coral Sarcodictyon roseum of Sarcodictyin C, D, E, and F, novel diterpenodic alcohols esterified by (E)‐ or (Z)‐N(1)‐methylurocanic acid. Failure of the carbon‐skeleton type as a classification criterion

It is shown here that the stoloniferan coral Sarcodictyon roseum of east Pyrenean waters contains four novel diterpenoids, sarcodictyin C ((−)‐3), D ((−)‐4), E ((+)‐5), F ((+)‐6), which are related to sarcodictyin A ( = (−)‐(4R,4aR,7R,10S,11S,12aR,1Z,5E,8Z‐7,10‐epoxy‐3,4,4a,7,10,11,12,12a‐octahydro‐7‐hydroxy‐6‐(methyoxycarbonyl)‐1,10‐dimethyl‐4‐(1‐methylethyl)‐benzocyclodecen‐11‐yl (E)‐N1‐methylyrocanate; ((−)−1), previously isolated from the same coral. Sarcodictyin C ((−)‐3) and D ((−)‐4) and the 3α‐hydroxy and 3α‐acetoxy derivatives of (−)‐1), sarcodictyin E ((+)‐5) is the (Z)‐urocanate isomer of (−)‐3), and sarcodictyin F ((+)‐6) is the 1α‐hydroxy‐2‐ene isomer of (−)‐3. In all cases, the nine‐membered ring is locked, and the molecule stabilized, by the urocanic appendage; when this is removed in MeOH/KOH, the C(11)–O− function is free to attack at C(5), and retro‐condensations then lead to the ring‐contracted butenolides 11 (from (−)‐3) or 10 (from(−)‐1) with extrusion of the hydroxyfuran nucleus (Scheme 3). Under the same conditions, with (−)‐3, the C(3)‐O− group competitively attacks at C(5), the hydroxyfuran nucleus is expelled, and aldehyde 14 is formed. Peculiarly, in the reaction of (−)‐3 with MeOD/KOD, the ring‐contracted butenolide 17 contains D at the 4′‐ax position. The sarcodictyins are unique in these chemical properties, not shared by the cladiellanes which have the same C‐skeleton.