STRUCTURE AND STEREOCHEMISTRY OF CONSTANOLACTONES A-G, LACTONIZED CYCLOPROPYL OXYLIPINS FROM THE RED MARINE ALGA CONSTANTINEA SIMPLEX

Extracts of the Oregon marine alga Constantinea simplex were found to contain a mixture of omega 6 and omega 3 unsaturated constanolactones, lactonized cyclopropyl-containing metabolites that logically derive f rom arachidonic and eicosapentaenoic acids, respectively. Detailed spe ctroscopic analysis of the isolated compounds, as natural products and various ester derivatives, afforded the planar structures of seven st ructurally related constanolactones. Constanolactones A-D possess 1,4- diol functionalities while constanolactones E-G contain a vicinal diol functionality. The absolute stereochemistry at all stereocenters in c onstanolactones A-D and at two stereocenters in constanolactones E and F were determined by chiral chromatography of fragments and chiroptic al measurements of various mono- and dibenzoate derivatives and by com parable rotations within the two series (A-D and E-G). Isolation of th ese various diastereomeric diols, as well as of two presumed methanol adducts from CHCl3/MeOH extraction of C. simplex, leads us to speculat e on the occurrence of highly unstable allylic epoxides in this red al ga.