Drug Metabolism in Drug Design and Development Basic Concepts and Practice

mass loss from the molecular ion can be used to specifically detect various
conjugated metabolites. For examples, glucuronides, sulfates, and glutathione
conjugates are often detected through CNL of 176, 80, and 129 Da,
respectively. Characteristic neutral losses of common Phase II conjugates are
listed in Table 11.2 (Levsen et al., 2005). The PIS and CNLS experiments only
record them/zvalues of metabolite ions showing predefined modification. To
obtain detailed structural information, full scan product ion spectra are
required for each metabolite. Unique fragment ions are then used to determine
structural differences between the parent molecule and related metabolites.
However, should a metabolite undergo a modification that alters the mass of

TABLE 11.2 Characteristic neutral losses from common Phase II conjugates under
collision-induced dissociation.

Conjugation
reaction/
conjugation with

Mass

shift

Characteristic

neutral loss

Mass of

neutral loss

Acetylation 42 Ketene (CH 2 ¼C¼O) 42
Glycine 57 Glycine 75
CO + H 2 O46
Sulfatation 80 SO 3 80
Cysteine 119 Cysteine 121
Alanine 89
Formic acid 46
N-Acetylcysteine 161 N-Acetylcysteine 163
N-Acetyl-2-iminopropionic
acid

129

Acetamide 59
Ketene 42
Glucosidation 162 Anhydroglucose 162
Glucose 180
Cysteine–glycine 176 Cysteine–glycine 178
Alanine–glycine 146
Glycine 75
Glucuronidation 176 Anhydroglucuronic acid 176
Glucuronic acid 194
N-Acetylglucosamine 203 Anhydro-N-acetylglucosamine 203
N-Acetylglucosamine 221
Glutathione 305 Glutathione 307
Glutathione – 2H 305
g-Glu-Ala-Gly 275
g-Glu-Ala-Gly – 2H 273
Glutamine 146
Anhydroglutamic acid 129
Glycine 75

336 APPLICATION OF LIQUID CHROMATOGRAPHY/MASS SPECTROMETRY