Lysine-selective reductive amination can be achieved catalytically by a supramolecular gallium cluster (Scheme 16B). For small molecule substrates, a gallium cluster Ga4L6 (L = N,N′-bis(2,3dihydroxybenzoyl)-1,5-diaminonaphthalene) host were known to cause catalytic Nazarov cyclization and aza-Darzens reactions through assembly of reaction components by hydrophobic effect and stabilization of cationic intermediates (i.e., electrostatic stabilization of cations by the polycationic host Ga4L6). Even for peptide and protein bioconjugation purposes, the same anionic gallium cluster can serve as a supramolecular host to catalyze reductive amination reactions on alkylamine groups of lysine residues. The specificity to lysine residues for the supramolecular catalysis contrasts with traditional reductive amination with a borohydride reagent (e.g., NaCNBH3), which often cannot differentiate lysine and N-terminal amines unless there is precise pH control. The selectivity mechanism was not studied in this report, but the supramolecular catalyst's preference toward sterically more accessible ε-amine may be the reason for the observed phenomena.