hydrogen/deuterium exchange (H/D exchange) of cross-linkable α-amino acid derivatives with deuteratedtrifluoromethanesulfonicacid (TfOD). H/D exchange with TfOD was easily applied to o-catechol containing phenylalanine (DOPA) within an hour. A partial H/D exchange was observed for trifluoromethyldiazirinyl (TFMD) phenylalanine derivatives. N-Acetyl-protected natural aromatic α-amino acids (Tyr and Trp)