These alkaloids have a phenyl or phenylpropyl nucleus. The group includes simple phenyl amine (tyramine, hordenine), catecholamine (dopamine, nora-drenaline, adrenaline), simple tetrahydroisoquinoline (mescaline, anhalamine, anhalonine, anhalonidine), benzylisoquinoline (e.g., papaverine), phthalideiso-quinoline (e.g., noscapine), phenethylisoquinoline (autumnaline, floramultine and kreysigine), tetrahydroisoquinoline (emetine and cephaeline) and terpenoid tetrahydroisoquinoline (secologanin and ipecoside) alkaloids.
The a for this group of alkaloids is L-tyrosine (in some cases, also phenylalanine) and the ft is L-dihydroxyphenylalanine (l-DOPA). Simple phenylamines, such as tyramine and hordenine, are derived from a by PLP (Figure 63). The A is tyramine and by activity of the SAM its P is hordenine. Phenyl and phenyl-propyl alkaloids form a very large and diverse group. Many of the compounds belonging to them have very important commercial implications and are used in pharmacology and medicine. The alkaloids from Amaryllidaceae (e.g., norbella-dine, lycorine, crinine and galanthamine) are also considered to be a part of this large group, although they are structurally very different. However, the pattern of biosynthesis, especially for a, is the same as for other alkaloids in this large group32. The term "isoquinoline alkaloids" was previously used for the group of phenyl and phenylpropyl alkaloids18.
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