Stereochemical analysis of natural products: alkaloids from the root bark of Strychnos panganensis

The possibilities of reliable determination of spatial structures of natural products based on correlation of high-level calculated and experimental ¹H and ¹³C NMR chemical shifts are considered using the example of four main representatives of the panganensine series, Strychnos-Strychnos type bisindole alkaloids. For isomeric panganensines X and Y, the reassignment of a number of individual NMR signals together with the spectral assignment of experimentally unresolved peaks is suggested, which allows the establishment of the absolute configuration for C-19, the only out-of-ring asymmetric carbon atom.