Stereoselective Preparation of the Tricyclic Hexasubstituted Spirocyclopropane Core of Cyclohelminthol X

This study focused on synthesizing the tricyclic hexasubstituted spirocyclopropane-core framework 2 of cyclohelminthol X (1), an antifungal cytotoxin isolated from Helminthosporium velutinum yone96 in a stereoselective manner. The synthesis features an SN2-type cyclopropanation of the quaternary chloride 23 generated via a retro-Michael-type ring-opening reaction of an 8-azatricyclo[4.3.0.12,5]deca-3,7,9-trione derivative 22. The successful synthesis confirmed the structure of 1, resolving the ambiguity from the absence of X-ray crystallographic analysis. The prepared models exhibited potent cytotoxicity.