In this disclosure, we summarize the preliminary metabolic profiling of the PI3Kδ inhibitor CDZ173 (leniolisib, 1a) obtained from incubations of the unlabeled compound and the synthesis of its metabolically stable tritium isotopologue 1b used for metabolite structure confirmation. Access to 1b was achieved when a halogenated precursor was subject to Hal/3H‐exchange. Hence, [3H]CDZ173 with specific activity 630 GBq/mmol, HPLC‐RA 97% and ee = 99.2% was obtained. Synthetic key to the precursor was using a bis‐halo‐pyridine in a Pd‐catalyzed mono‐amination of the tetrahydropyrido‐pyrimidine core. Stereochemistry of the synthetic precursors were confirmed by X‐ray analysis of the unlabeled bis‐halo‐pyridines and chiral HPLC of the tritiated material. The correct position of tritium label in the target, was confirmed by 3H‐NMR difference spectroscopy. Besides, we report on the validation of the radiotracer as a tool for pre‐clinical ADME in incubations with hepatocytes. Based on this data, we present a quantitative metabolite profile of leniolisib which was confirmed by independently synthesized metabolite references. The conformation of CDZ173 was investigated by NMR suggesting two different amide backbones each with specific pyrrolidine puckerings.

Drug metabolism studies are performed in drug discovery to identify metabolic soft spots, detect potentially toxic or reactive metabolites and provide an early insight into potential species differences. The relative peak area approach is often used to semi-quantitatively estimate the abundance of metabolites. Differences in the liquid chromatography-mass spectrometry responses result in an underestimation or overestimation of the metabolite and misinterpretation of results. The relative MS response factors (RF) of 132 structurally diverse drug candidates and their 233 corresponding metabolites were evaluated using a capillary-liquid chromatography/high-resolution mass spectrometry system. All of the synthesized metabolites discussed here were previously identified as key biotransformation products in discovery investigations or predicted to be formed. The most commonly occurring biotransformation mechanisms such as oxygenation, dealkylation and amide cleavage are represented within this dataset. However, relatively few phase II metabolites were evaluated because of the limited availability of authentic standards. Approximately 85% of these metabolites had a relative RF in the range between 0.2 (fivefold under-prediction) and 2.0 (twofold over-prediction), and the median MS RF was 0.6. Exceptions to this included very small metabolites that were hardly detectable. Additional experiments performed to understand the impact of the MS platform, flow rate and concentration suggested that these parameters do not have a significant impact on the RF of the compounds tested. This indicates that the use of relative peak areas to semi-quantitatively estimate the abundance of metabolites is justified in the drug discovery setting in order to guide medicinal chemistry efforts. Copyright © 2017 John Wiley & Sons, Ltd.

LC-MS based drug metabolism studies are effective in the optimization stage of drug discovery for rapid partial structure identification of metabolites. However, these studies usually do not provide unambiguous structural characterization of all metabolites, due to the limitations of MS-based structure identification. LC-MS-SPE-NMR is a technique that allows complete structure identification, but is difficult to apply to complex in vivo samples (such as bile collected during in vivo drug metabolism studies) due to the presence, at high concentrations, of interfering endogenous components, and potentially also dosage excipient components (e.g. polyethylene glycols). Here, we describe the isolation and structure characterization of seven metabolites of the drug development candidate 1-isopropyl-4-(4-isopropylphenyl)-6-(prop-2-yn-1-yloxy) quinazolin-2(1H)-one from a routine metabolism study in a bile-duct cannulated rat by LC-MS-SPE. The metabolites were isolated from bile and urine by repeated automatic trapping of the chromatographic peak of each metabolite on separate Oasis HLB SPE columns. The micropreparative HPLC/MS was performed on an XBridge BEH130 C18 HPLC column using aqueous formic acid/acetonitrile/methanol as mobile phase for the gradient elution. Mass spectrometric detection was performed on a LTQ XL linear ion trap mass spectrometer using electrospray ionization. Desorption of each metabolite was performed after the separation sequence. NMR spectra ((1)H, (13)C, 2D ROESY, HSQC and HMBC were measured on a Bruker AVANCE III spectrometer (600 MHz proton frequency) equipped with a 1.7 mm (1)H{(13)C,(15)N} Bruker Biospin's TCI MicroCryoProbe™.