Eugeniifoline, a Pentacyclic Indole Alkaloid from Leuconotis eugeniifolia , and Configurational Revision of Synthetic Eugeniifoline Isolated from a Diversity-Enhanced Extract.

Eugeniifoline ( 1 ), a pentacyclic indole alkaloid with a five-membered ring E, was isolated for the first time as a natural product from the stem-bark extract of Leuconotis eugeniifolia . Eugeniifoline ( 1 ) was previously reported as a synthetic product from a diversity-enhanced extract, but with the configuration at C-21 reported as S ( 1a ). The configuration at C-21 was revised to R as shown in 1 , based on the NOE data, GIAO NMR calculations, and DP4+ probability analysis, as well as the TDDFT-ECD method.