Structural and stereochemical reassessment of sclerophytin-type diterpenes

Marine invertebrates are a rich source of oxygenated diterpenoids.(1-4) Among those isolated from the soft coral Sclerophyturn capitalis are sclerophytins A and B, originally formulated by their discoverers as 1 and 2.(5) The novel structural features of these oxygen-bridged heterocycles and the significant cytotoxic properties of 1 have attracted some defining synthetic work.(6-9) In consideration of the fact that synthetic 3 and 4 both proved to differ significantly from the originally isolated marine metabolites, an extensive N'MR analysis of 2 was undertaken, the results of which identified sclerophytin B to be 6.(10) This thorough investigation also implicated sclerophytin A to be 5 since its simple acetylation leads to 6.(5,7,8).