Configurational and Conformational Studies of Quinolizidine and <i>Beta</i>‐Carboline Moieties in the <i>Corynanthe‐Tryptamine</i> Alkaloids

ABSTRACT Configurational and conformational assignments of 11 Corynanthe‐Tryptamine alkaloids (usambarane skeleton) were performed based on the correlation of the high‐level calculated and experimental 1 H and 13 C NMR chemical shifts. For some compounds, the reassignment of a number of individual signals together with spectral assignment of experimentally unresolved peaks was suggested. The different conformations of the C/D quinolizidine ring system appear strictly dependent of the structure of the side chain (ethyl‐, vinyl‐ or ethylidenic); in the latter case, the configuration ( E or Z ) of the 19‐20 double bond of the ethylidenic chain is determinant to establish a cis‐ or a trans ‐quinolizidine system of rings C/D. The conformation is also influenced by the equatorial or axial conformation of (C15) substituents.