The BU anionophores presented in this work were obtained utilizing a macrocyclization reaction of glycolurils (GU) and formaldehyde in the presence of sulphuric acid, which acted both as an acid catalyst and a source of HSO4 -as template, promoting the formation of a six-membered macrocycle (Figure ). The GU building blocks were prepared using one of the two synthetic strategies shown in Figure . In the first strategy (Path A), a substituted benzylamine was used as the starting material. It was first reacted with diphenyl carbonate to give a symmetric 1,3-disubstituted urea. The urea was then condensed under acidic conditions with 4,5-dihydroxyimidazoline, leading to a GU. When a substituted benzyl halide (chloride or bromide) was used as the starting material, this was reacted with a GU bearing two para-methoxybenzyl (PMB) protecting groups under basic conditions (Path B). The PMB groups were subsequently cleaved using ceric ammonium nitrate. The GU building blocks for BUs 1 and 6-8 were prepared using Path A; Path B was used to prepare GU building blocks for BUs 2-5 and 7. GU building blocks for BUs 9 and 10 were prepared by oxidation of the GU building block for BU 7. GU building blocks for BUs 11 and 12 were prepared by functionalization of GU bearing para-hydroxybenzyl groups with triflyl or mesyl groups, respectively. BUs 6, 8 and 11 are prepared as new compounds and their detailed synthetic procedures and characterisation can be found in the ESI (Section 1).