In vivo study on biotransformation of pentacyclic analogs of progesterone: Identification of their metabolites by HPLC-MS method

Progesterone derivatives containing the D' additional cyclohexane ring in the 16 alpha,17 alpha-positions of steroid core (pregna-D'-pentaranes) exhibited high in vitro and in vivo selective progestogenic activity. The assessment of their biotransformation in the body, and the identification of possible metabolites are integral parts of a potential drug studies. Here we describe the results of in vivo metabolic transformation of 6 alpha-methyl-16 alpha,17 alpha-cyclohexanopregn-4-ene-3,20-dione 1 and its 6-demethylated analog 2 and identification of their metabolites in rat urine. We synthesized and fully characterized (1D and 2D NMR, HRMS) 11 possible metabolites as the standards. Then we developed the LC-MS/MS assay including sample preparation and chromatography conditions for identification of the detected metabolites of 1 and 2. The 5 alpha- and 5 beta,20-diketo-, 3 beta-hydroxy-20-keto-5 alpha-, 3-keto-20(S)-hydroxy-5 alpha-, 3 beta,20(S)-dihydroxy-5 alpha-ametabolites of compounds 1 and 2 were found in rat urine samples. The starting steroids 1 and 2, as well as both 313,20(R)-dihydroxy metabolites were not detected in the examined biological urine samples. Thus, we demonstrate for the first time that exogenous progestines - pregria-D'-pentaranes-and endogenous progesterone follow similar metabolic pathways. Therefore, despite the presence of an additional ring D' and the methyl group in position 6, the main enzymatic transformations are similar to those of the natural hormone.