Identification, synthesis, and characterization of a unique N-glucuronide of an acid metabolite of camizestrant (AZD9833) in humans

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Camizestrant (AZD9833) is a next-generation oral selective estrogen receptor (ER) degrader and complete ER antagonist in phase 3 clinical development for the treatment of ER-positive breast cancer. Metabolite M14, an N-glucuronide of the acid metabolite M46 of camizestrant, is one of the major circulating metabolites in humans, in addition to a direct N-glucuronide M4. In light of the fact that the existence of the acidic functional group of the acid metabolite M46 prevented an efficient in vitro glucuronidation in human liver microsomes, a novel hybrid chemical and biological synthesis of AZ4678 (M14) was successfully achieved. The acidic functional group of AZ8713 (M46) was esterified with methanol to give the M46 methyl ester, which was then glucuronidated in human liver microsomes in the presence of UPDGA to form M14 methyl ester. Selective hydrolysis of M14 methyl ester by aqueous lithium hydroxide in tetrahydrofuran successfully generated AZ4678 (M14). The development of this synthesis route has introduced a new approach to synthesizing glucuronides of compounds with acidic functional groups that otherwise interfere with their susceptibility to glucuronidation. NMR analysis confirmed the structure of AZ4678 (M14) with the glucuronic acid attached to the position N45 of the azole nitrogen atom while retaining the original stereochemistry of camizestrant. Chromatography of AZ4678 (M14) was sensitive to 67% of organic content in samples as well as sensitive to solvents at a basic pH containing ammonium hydroxide, resulting in split peaks in liquid chromatography-mass spectrometry analysis. AZ4678 (M14) was stable in human feces and in aqueous solutions at a pH range of 1.5-12.0. SIGNIFICANCE STATEMENT: Metabolite M14 of camizestrant (AZD9833), a major circulating metabolite in humans, was successfully identified as an N-glucuronide of an acid metabolite of camizestrant, and its unusual chromatographic and stability properties were characterized. The development of a novel hybrid chemical and biological synthesis for M14 has introduced a new approach to synthesizing glucuronides of compounds with acidic functional groups that otherwise interfere with their own in vitro glucuronidation.