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

[Display omitted] •Biotransformation of 6α-methyl-16α,17α-cyclohexanoprogesterone (mecigestone) and its 6-demethylated analog in rats was studied.•These 16α,17α-cyclohexane derivatives of progesterone (pregna-D'-pentaranes) metabolize like the natural hormone.•5β-, 5α-, 3β-Hydroxy-5α-, 20-hydroxy-5α-, 3,20-dihydroxy-5α-metabolites in urine samples were identified by HPLC-MS method.•11 Metabolite standards were synthesized. Progesterone derivatives containing the D' additional cyclohexane ring in the 16α,17α-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 6α-methyl-16α,17α-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 5α- and 5β-3,20-diketo-, 3β-hydroxy-20-keto-5α-, 3-keto-20(S)-hydroxy-5α-, 3β,20(S)-dihydroxy-5α-metabolites of compounds 1 and 2 were found in rat urine samples. The starting steroids 1 and 2, as well as both 3β,20(R)-dihydroxy metabolites were not detected in the examined biological urine samples. Thus, we demonstrate for the first time that exogenous progestines - pregna-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.