REGULAR AND IRREGULAR SESQUITERPENES CONTAINING A HALOGENATED HYDROPYRAN FROM LAURENCIA CAESPITOSA

Article abstract of DOI:10.1016/S0031-9422(00)97759-8

The red seaweed Laurencia caespitosa is an unusually rich source of secondary metabolites.Five novel regular and irregular halogenated sesquiterpenes were isolated and characterized from this alga.The laucapyranoids A, B and C form a new class of rearranged terpenoids.The structures of laucapyranoids A and B were established by 1D and 2D NMR experiments, the latter being confirmed by X-ray crystallography.The identify of the unstable laucapyranoid C was established by reconstruction of its hydrodebrominated derivatives, whose structures were determined by spectroscopic data and X-ray analysis.The structures of the regular sesquiterpenoids 6-hydroxy-caespitol and caespitane were elucidated from spectroscopic data and confirmed by X-ray analysis in the case of caespitol and isocaespitol.Finally, the exciton chirality method was applied to the determination of the absolute configuration of caespitol and isocaespitol.The circular dichroism allylic benzoate approach circumvented the problems associated with the Bijvoet X-ray diffraction method in a previous study of these sesquiterpenes. - Keywords: Laurencia caespitosa; Rhodomelaceae; halogenated sesquiterpenes; laucapyranoids; 6-hydroxy-caespitol; caespitane; caespitol; isocaespitol.