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Covering: up to the end of March 2010 Unlike the majority of terpenoids, a significant fraction of the polycyclic diterpenoids (∼7000 already known) are now understood to originate from dual, rather than single, biosynthetic cyclization and/or rearrangement reactions, which proceed via a bicyclic diphosphate intermediate. The trivial name for the hydrocarbon skeleton of the most commonly found version of this biosynthetic intermediate forms the basis for a unifying “labdane-related” designation for this large super-family of natural products. Notably, many of these are found in plants, where the requisite biosynthetic machinery for gibberellin phytohormones, particularly the relevant diterpene cyclases, provides a biosynthetic reservoir that appears to have been repeatedly drawn upon to evolve new labdane-related diterpenoids. The potent biological activity of the “ancestral” gibberellins, which has led to the …