Spiroamentotaxols A–D: unprecedented 6/6/6/5/6/6/6/6 spiro-octacyclic bis-diterpene heterodimers from the endangered conifer Amentotaxus yunnanensis and their bioactivities

As a new chemical class of bis-diterpene heterodimers, spiroamentotaxols A–D (1–4) are characterized by a complex 6/6/6/5/6/6/6/6 spiro-octacyclic ring system, which is likely biogenetically derived from a Diels–Alder [4 + 2] cycloaddition between an ent-kaurene and a C20-norabietane. The spiroament...

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