SSAs 1 and 2 in addition to anion transporter 4 were synthesised in line with previously published methods. 15b, 16 SSA 3 was synthesised through the reaction of tetrabutylammonium (TBA) aminomethanesulfonate with 2-aminobenzothiazole and 1,1'carbonyldiimidazole (CDI), which gave the desired product as a white solid in a yield of 92% (see Section S1).