Design of A Metabolically Stable Tritium-Tracer of the PI3Kδ-Inhibitor CDZ173 (Leniolisib) as a Tool to Study Liver Metabolites

In this disclosure, we summarize the preliminary metabolic profiling of the PI3K 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/H-3-exchange. Hence, [H-3]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 H-3-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.