Total Syntheses, Absolute Configuration, and Cytotoxicity Evaluation of Ugonins L, S, U, and Z from the Rhizomes of Helminthostachys zeylanica

This study describes the first and efficient syntheses of naturally occurring ugonins L (1a), S (2a, 2b), U (3), and Z (4). Naturally occurring ugonin S has two stereoisomers. On the basis of their NMR and specific rotation data, the absolute configuration of trans-ugonin L (1a) was determined as 10R,11R, while the absolute configurations of trans-ugonin S (2a) and cis-ugonin S (2b) were determined to be 10R,11R and 10R,11S, respectively. The naturally occurring cis-ugonin U (3) presented the 10S,11R configuration. The naturally occurring cis-ugonin Z (4) was suggested to have a 10S,11R configuration. Four isomers of compound 2 and two isomers of compound 3 showed moderate cytotoxic activities against the CEM and H460 human cancer cell lines.