Secodine-type alkaloid

This biogenetic proposal has spurred interest in the synthesis of structures such as (70). An especially efficient example of the use of intramolecular Diels-Alder reactions to synthesize aspidosperma alkaloids has been developed by Kuehne and co-workers <8373715, 85JOC924, 85JOC4790, 87JOC347). The azepino[4,S-6]indole structure (72) is condensed with a d-haloaldehyde generating (74), which undergoes fragmentation to (75) which contains the secodine synthon. With the secodine type structure only cycloaddition path b is available and aspidosperma structures are formed (76) (Scheme 148). 

Hajicek J. A review on recent developments in syntheses of the post-secodine indole alkaloids. Part I the primary alkaloid types. Collect. Czech. Chem. Commun. 2004 69 (9) 1681-1767. 

If the C-15, C-16 bond is oxidatively cleaved, the secodine skeleton results (the proposed progenitor of the Aspidosperma and the iboga systems) through alternative Diels-Alder type cyclizations to afford tabersonine and catharanthine. The bisindole alkaloids of Catharanthus roseus reflect the union of vindoline and catharanthine to afford anhydrovinblastine modification affords the clinically significant alkaloids, vinblastine (VLB) and vincristine (VCR Fig. 39). The alkaloids, particularly VCR, are important as anticancer agents and have led to the development of the semisynthetic derivatives vindesine and vinorelbine (Fig. 40). Synthetic approaches are available to join the monomeric precursors. The enzymatically controlled sequence of reactions from tabersonine to vindoline has been elucidated. 

Secodine Group. In the biogenetic interrelationship of the three major mono-terpene-tryptamine alkaloid types, i.e. strychnos, aspidosperma, and iboga, the necessary changes in the aliphatic skeleton can be schematically represented... 

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