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 ( = (−)‐(4 R ,4a R ,7 R ,10 S ,11 S ,12a R ,1 Z ,5 E ,8 Z ‐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 )‐ N 1 ‐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.