ANTIPODAL PATHWAYS TO SECONDARY METABOLITES IN THE SAME EUKARYOTIC ORGANISM

Rogioldiol B ((-)-3) and rogioldiol C ((-)-7) were isolated from the e i red seaweed Laurencia microcladia. which grows at Il Rogiolo along t he coast of Tuscany, as the first examples of 15.14-friedoobtusane dit erpenes. The absolute configuration at their brominated moiety was ass umed to be identical to rogiolal (2), already isolated from the same s eaweed as a putative biodegradation product of rogioldiol A ((-)- 1), Failure to define the absolute configuration through investigation of Mosher's esters reflects a so far unrecognized problem of sterically c rowded secondary alcohols in acyclic systems. However, the absolute co nfiguration at C9, defined by exciton-coupling techniques. could be ex tended to C10 by extensive NMR experimentation and molecular mechanics calculations, Surprisingly (-)-3 and (-)-7 have the opposite configur ation at C10, which suggests that they are formed along two different biogenetic pathways involving mirror-image folding of a geranyl gerani ol-derived precursor.