P-Carboline alkaloids

Acylation of 3-substituted indoles is more difficult, however 2-acetylation can be effected with the aid of boron trifluoride catalysis." " Indoles, with a carboxyl-containing side-chain acid at C-3, undergo intramolecular acylation forming cyclic 2-acylindoles." Intramolecular Vilsmeier processes, using tryptamine amides, have been used extensively for the synthesis of 3,4-dihydro-p-carbolines, a sub-structure found in many indole alkaloids (P-carboline is the widely used, trivial name for pyrido[3,4-fc]indole). Note that it is the imine, rather than a ketone, that is the final product the cyclic nature of the imine favours its retention rather than hydrolysis to amine plus ketone as in the standard Vilsmeier sequence " this ring closure is analogous to the Bischler-Napieralski synthesis of 3,4-dihydro-isoquinolines (9.15.1.7). 

Biogenesis of manzamine alkaloids (P-carboline marine alkaloids) 97YGK1114. 

Conducted in an intramolecular sense, both Mannich and Vilsmeier reactions have been much used for the construction of tetrahydro-p-carbolines (dihydro-P-carbolines), such as are found in many indole alkaloids (p-carboline is the widely used, trivial name for the pyrido[3,4-Z ]indole nucleus). 

Figure 1.29 Examples of Mannich reactions, (a) Biosynthesis of alkaloids bearing the 1,2,3,4-tetrahydroisoqumoline ring, (h) biosynthesis of indole alkaloids (P-carboline, 3,3-spiroindolenine), and (c) tropinone biosynthesis.

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , , ]

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