Ammonium acetate

High-performance liquid chromatography-grade water, methanol, and acetonitrile (ACN) were from J.T. Baker (Phillipsburg, NJ, USA). Analytical-grade formic acid and ammonium acetate and the internal standard (cholic acid-d5), were purchased from Toronto Research Chemicals (Toronto, Canada). Authentic chemicals for establishing the in-house database were purchased from Sigma-Aldrich (St. Louis, MO, USA).

Saxagliptin, trelagliptin, and gemigliptin (Figure 1) were purchased from AdooQ Bioscience (>98%, Irvine, CA, USA); linagliptin and 5-hydroxySaxagliptin from Toronto Research Chemicals (Toronto, Canada); ammonium acetate (99.99%), β-nicotinamide adenine dinucleotide phosphate sodium salt hydrate (NADP⁺), dimethyl sulfoxide (DMSO, >99.7%), glucose-6-phosphate (G6P), glucose-6-phosphate dehydrogenase (G6PD), L-cysteine, magnesium chloride, reduced glutathione (GSH, ≥99%), 3′-phosphoadenosine-5′-phosphosulfate (PAPS), potassium phosphate, uridine diphosphate glucuronic acid (UDPGA, >98%), and vildagliptin from Sigma-Aldrich (St. Louis, MO, USA); and rat liver microsomes (RLM, R1000) from XenoTech (Lenexa, KS, USA). All solvents were LC-MS grade from Fisher Scientific (Pittsburgh, PA, USA).