Biosynthesis of isoquinoline alkaloids.

Abstract

The isoquinoline alkaloids and their biosynthetic relatives include many compounds which show important physiological properties in animals: dopamine, mescaline, morphine, papaverine, and narcotine are pertinent examples. The biosynthetic routes to the members of this family start from the essential aminoacids tyrosine or phenylalanine. Decarboxylation gives a phenethylamine building block (C6–C2) which then combines with an additional building block to form an isoquinoline ring. This stage of the general biosynthetic scheme is illustrated by the biosynthesis of the cactus alkaloid anhalonidine. Many important classes of alkaloid are produced by further transformation of simple isoquinoline systems. In the opium poppy the benzylisoquinoline reticuline is converted to the two very different alkaloids morphine and narcotine. More recently it has been estblished that two of the alkaloids of Stephania, japonica, protostephanine and hasubanonine are also produced by modification of a benzylisoquinoline precursor. These varied biosynthetic pathways and the methods used in their elucidation are discussed in detail.