Truncated LctA mutants containing nonproteinogenic amino acids prepared by Cu(I)-catalyzed triazole cycloaddition (C6 triazole) and the results following incubation with LctM in the presence of Mg2+ and ATP, as analyzed by MALDITOF MS. The side chains (R1) for α-amino acids in entries 19-25 are shown. Substrates that resulted in complete modification following LctM incubation are depicted in bold, whereas those that resulted in incomplete conversion or no reaction are shown in italics. NR, no reaction.