Identification of selective inhibitors of sphingosine kinases 1 and 2 through a structure–activity relationship study of 4-epi-jaspine B

We recently reported that 4-epi-jaspine B exhibits potent inhibitory activity towards sphingosine kinases (SphKs). In this study, we investigated the effects of modifying the 2-alkyl group, as well as the functional groups on the THF ring of 4-epi-jaspine B using a diversity-oriented synthesis approach based on a late-stage cross metathesis reaction. The introduction of a p-phenylene tether to the alkyl group was favored in most cases, whereas the replacement of a carbon atom with an oxygen atom led to a decrease in the inhibitory activity. Furthermore, the introduction of a bulky alkyl group at the terminus led to a slight increase in the inhibitory activity of this series towards SphKs compared with 4-epi-jaspine B (the Q values of compound 13 for SphK1 and SphK2 were 0.2 and 0.4, respectively). Based on this study, we identified two isoform selective inhibitors, including the m-phenylene derivative 4 [IC₅₀ (SphK1) ≥30 μM; IC₅₀ (SphK2) = 2.2 μM] and the methyl ether derivative 22 [IC₅₀ (SphK1) = 4.0 μM; IC₅₀ (SphK2) ≥30 μM].