Synthesis of linkage isomers bead-linker-AA2-AA1-1-AA1-AA2. PS, polystyrene; EBES, 2,2′-(ethylenedioxy)bis(ethylamino) monosuccinimide; Boc, t-butoxycarbonyl; Fmoc, fluorenylmethoxycarbonyl; DMF, dimethylformamide; DIC, N,N′-diisopropylcarbodiimide; HOBt, hydroxybenzotriazole; DIEA, N,N-diisopropylethylamine.