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.
Financial support was provided by grants MAREX [FP 7; KBBE–3-245137 (EU)], SAF2011-28883-03-01 and SAF2008-02251 (MICINN); RD06/0020/1037 from Red Temática de Investigación Cooperativa en Cáncer, Instituto de Salud Carlos III, co-funded by the Fondo Europeo de Desarrollo Regional of the European Union, and Junta de Castilla y León (CSI052A11-2, and GR15-Experimental Therapeutics and Translational Oncology Program). F.C.P. acknowledges a repatriation fellowship (Consejo Nacional de Ciencia y Tecnología; 168081) and SEGAI-ULL fellowship.