Based on highly active transporter 1, we have recently reported the synthesis and evaluation of the anion binding properties of BUs 2-5. These thioether derivatives are predicted to be more lipophilic than the parent BU 1 (see Table ) and the lipophilicity of these derivatives is increased by extending the length of the fluoroalkyl chains on the BU benzyl substituents, going from -SCF3 to -SC2F5 and -SC3F7 groups for BUs 2, 3 and 4, respectively. BU 5 resembles BU 2 but with addition of a -OMe group on the benzyl substituent, which did however not change the anion binding strength, and the calculated logP values for BUs 2 and 5 suggest that the lipophilicity is not significantly impacted either.