Expanding peptide-cucurbit[7]uril interactions through selective N-terminal reductive alkylation

Cucurbit[7]uril (CB[7]) is a supramolecular binding host for peptides and proteins with N-terminal Phe. However, the low occurrence of such peptides and proteins limits broader applications of this unique host-guest interaction. Here, we report a strategy to expand the scope of CB[7]-peptide interaction by site-specifically introducing N-terminal substitutions (e.g. benzyl groups) using reductive alkylation. N-terminal benzylated peptides have similar affinity to CB[7] as native peptides with N-terminal Phe and even stronger interactions can be achieved using better ligands. We further expanded this host-guest interaction to be stimuli responsive. By introducing benzyl carboxylate substituents, the CB[7]-peptide interaction shows pH-dependent binding. Furthermore, benzyl boronate substituents led to saccharide-dependent CB[7]-peptide interactions. We demonstrated that using this strategy to introduce stronger CB[7] binders to the N-terminus of human calcitonin (hCT) results in increased aggregation stability in the presence of CB[7]. This strategy to expand CB[7]-peptide interaction scope opens opportunities for future applications in peptides and proteins.