Tryptophan monoterpene indole

Adina cordifolia has yielded a pair of jS-carboline acids, cordifoline" " (43) and adifoline (44), which are closely related to the vincosides in structural type. In both compounds the carboxy-group of precursor tryptophan is retained very few monoterpene indole alkaloids have been obtained which do still retain this feature, though of course, classical methods of alkaloid isolation would automatically lose such compounds in discarded acidic fractions. 

Tryptophan-Derived Indole and Indole Monoterpene Alkaloids As for alkaloids derived from tyrosine and phenylalanine, those derived from tryptophan are formed after decarboxylation of the amino acid (into tryptamine) and possible hydroxylation of the aromatic carbocycle (e.g., serotonin) and N-methylation (e.g., psilocin). As previously, tryptamine can also react through Pictet-Spengler reactions to form tetrahydro-p-carbolines, which can be aromatized, for example, into harmine (Scheme 1.8) [16]. 

Wishing to provide a deeper understanding of the synthetic tactics, which are used on the examples that will follow, some general guidelines on the design of a common synthetic scaffold are provided. These guidelines follow David W.C. MacMillan s tryptophan-derived monoterpene indole alkaloids syntheses as an example [39] ... 

Within the natural products field, the investigation of complete biosynthetic pathways at the enzyme level has been especially successful for plant alkaloids of the monoterpenoid indole alkaloid family generated from the monoterpene gluco-side secologanin and decarboxylation product of tryptophan, tryptamine [3-5]. The most comprehensive enzymatic data are now available for the alkaloids ajmalicine (raubasine) from Catharanthus roseus, and for ajmaline from Indian Rauvolfia serpentina [6] the latter alkaloid with a six-membered ring system bearing nine chiral carbon atoms. Entymatic data exsist also for vindoline, the vincaleucoblastin (VLB) precursor for which some studies on enzymatic coupling of vindoline and catharanthine exist in order to get the so-called dimeric Catharanthus indole-alkaloids VLB or vincristine [7-9] with pronounced anti-cancer activity [10, 11]. 

This is an example of a bicyclic ring system with the fusion of benzene and pyridine rings. Biosynthetically they are related to indole alkaloids since both groups are derived from the same two precursors, tryptophan and loganin—a monoterpene iridoid (Samuelsson 1992). 

This is a very large group of alkaloids whose basic structure contains a pyrrole ring fused to a benzene ring. Biosynthesis of pure indoles involves the amino acid tryptophan as precursor, while that of a major subgroup of the indoles, including the Catharanthus and Rauwolfia alkaloids, involves a second precursor— the monoterpene iridoid loganin. 

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