Modified Benzyltetrahydroisoquinoline Alkaloids

The condensation of dopamine (4) with phenylethyl units and subsequent cyclization result in the formation of benzyltetrahydroisoquinoline alkaloids. These initial reaction steps are identical to those discussed for the formation of simple tetrahydroisoquinoline alkaloids. However, the additional aromatic ring allows further modification, and a variety of structurally diverse classes of alkaloids are obtained via different aryl-aryl coupling reactions. Among others, protoberberine alkaloids, porphine alkaloids, and the most important class of opium alkaloids can be summarized as modified benzyltetrahydroisoquinoline alkaloids. 

The manifold possibilities for the elaboration of structurally intriguing natural products via the aforementioned oxidative aryl-aryl coupling reactions emphasize the importance of phenolic coupling reactions in the biosynthesis of tyrosine-derived alkaloids. This important reaction not only plays a significant role in the biosynthesis of benzyltetrahydroisoquinoline alkaloids but also for the construction of phenethylisoquinoline alkaloids and Amaryllidaceae constituents, discussed in the following sections. 

El Tyrosine transaminase E2 4-Hydroxyphenylpyruvic acid decarboxylase E3 Norcoclaurine syndiase 

E5 ( 5)-Coclaurine A -methyl transferase PLP E ridoxal E6 (5)-A -Methylcoclaurine 3 -hydroxylase phosphate E7 (5)-3 -Hydroxy-A -methylcoclaurine SAM 5-Adenosyl 4 -0-Methyl transferase methionine 

Alkaloids of the protoberberine skeleton as well as followup products have been isolated from various species of the Berberidaceae and the Ranunculaceae plant families [18]. 

---

Alkaloids Derived from Tyrosine Modified Benzyltetrahydroisoquinoline Alkaloids 407... 

---