Saiyacenols A and B: the key to solve the controversy about the configuration of aplysiols

Two new cytotoxic oxasqualenoids, saiyacenols A and B, were isolated from the red alga Laurencia viridis and their structures elucidated by spectroscopic methods and chemical correlation with the well-known compound dehydrothyrsiferol. The new compounds share an important part of their structure with thyrsiferol and aplysiols B and C. Isolation of the saiyacenols concludes the controversy about the configuration of aplysiols, correcting the structure of aplysiol B. Our results illustrate the current limitations of NMR J-based methods when approaching quaternary carbons and demand a reappraisal of rational biogenetic proposals in structural elucidation.