Fig. 5. Extracted ion chromatograms at m/z = 130.1590 ± 0.005 (corresponding to the [M + H]⁺ ion for 21) from UHPLC-ESI-Q-TOF-MS analyses of an authentic standard of 21 (top), the CpkG-catalyzed reaction of 14 with l-alanine (middle) and a control reaction from which the enzyme was omitted (bottom).