Synthesis and Antitumor Activity Evaluation of γ-Monofluorinated and y,y-Difluorinated Goniothalamin Analogues

A series of novel γ,γ-difluorinated Goniothalamin analogues 4a--4i and 6a--6i were synthesized. The key steps included the construction of C-5 stereocenter adjacent to gem-difluoromethylene group by way of lipase AK catalyzed kinetic resolution, the introduction of aryl group via Stille coupling, and lactonization by 1,5-oxidative cycli- zation. These γ,γ-difluorinated Goniothalamin analogues 4a-4i and their enanfiomers 6a--6i, together with several corresponding 7-monofluorinated Goniothalamin analogues were biologically evaluated against four different cancer cell lines. Compound 7h showed a nearly equivalent potency as the parent （R）-Goniothalamin in the micromolar range. The different fluorine effects between fluoromethylene and gem-difluoromethylene on antitumor activity were discussed through the analysis of bioassay data.