Neoisostegane, A New Bisbenzocyclooctadiene Lignan Lactone from Steganotaenia Araliacea¹

Neoisostegane, the first naturally occurring steganin without a functional group at C-5, was isolated from two different collections of Steganotaenia araliacea. The structure of neoisostegane, which contained five aromatic methoxyl groups rather than the more usual three methoxyls and one methylenedioxy moiety, was elucidated by comparison of the pmr coupling constants with those of synthetic steganes and by selective decoupling experiments. The structure was confirmed by cmr data, by preparation of a derivative having five aromatic methoxyl moieties from stegane, which was compared spectroscopically to neoisostegane, and by thermal isomerization experiments.