In this work, we have investigated the anion transport properties of twelve BU derivatives, only two of which have been previously studied and three of which were prepared for the first time. Measurements of their Cl -/HCO3 -antiport activities in the lucigenin assay provided a comprehensive study of the effect of variation of substituents on large macrocyclic anionophores on their transport properties. As the affinities of the tested BUs to anions are generally very high, the absolute Ka values seem not to be an important parameter, in contrast to what is commonly observed in the literature for smaller compounds. All tested BUs (apart from 12) are predicted to be highly lipophilic and further increases in the lipophilicity were found to have a negative impact on the transport abilities.