Chemistry, bioactivity, biosynthesis, and total synthesis of stemmadenine alkaloids

Covering: up to July 2022Stemmadenine alkaloids are a restrictive sub-group of monoterpene indole alkaloids, represented by two congeners: stemmadenine and vallesamine. Their skeleton is defined by the cleavage of the C-3-C-7 bond of the Strychnos group's pentacyclic scaffold in monoterpene indole alkaloids. The parent alkaloid stemmadenine acts as a key intermediate in the biosynthesis of several major monoterpene indole alkaloid families, including regular Strychnos alkaloids, Aspidosperma alkaloids, and Iboga alkaloids. In this review, a complete coverage of the stemmadenine alkaloids, from the early reports till the present day at 2022, are presented, and their diverse biological activities are briefly described. Moreover, the biosynthetic proposal for stemmadenine and the proposed biogenetic conversion of stemmadenine-type alkaloids into vallesamine-type congeners are discussed in detail. Moreover, the successful synthetic strategies to access the strained stemmadenine scaffolds are fully reviewed.