Structure–activity relationships of quassinoids for eukaryotic protein synthesis

The effect of 63 quassinoids on eukaryotic protein synthesis has been investigated. Seventeen of the tested compounds showed potent in vitro activity, with IC50s below 2 μM for inhibition in Krebs ascites translation extracts. Sixteen of these quassinoids were also potent inhibitors of in vivo protein synthesis when exposed to Hela cells for 1 h. Our results led to the following structure–activity relationships for quassinoids regarding translation inhibition. Activity is influenced by (i) the nature of the C-15 side chain, (ii) the nature of A ring modifications, (iii) the presence or absence of a sugar moiety, and (iv) the presence of an epoxymethano bridge.