Fig. 4. Extracted ion chromatograms at m/z = 187.2 (corresponding to the fragment ion of 16 resulting from loss of a methyl group) from GC-MS analyses of an authentic standard of 16 (top), the BSA-derivatized product of the CpkC-TR-catalyzed reduction of 13 with NADH (middle) and the BSA-derivatized product of a control reaction containing boiled enzyme (bottom).