New metabolic pathway of (24R)-24,25-dihydroxyvitamin D3: epimerization of the 3-hydroxy group

A new metabolic pathway of (24R)-24,25-dihydroxyvitamin D3 [24,25(OH)2D3] was clarified in the in vivo experiments. After the administration of 24,25(OH)2D3 to rats, a new monoglucuronide of a vitamin D metabolite was obtained from the bile together with 24,25(OH)2D3 3- and 24-glucuronides. The genin of the metabolite was identified as 3-epi-24,25(OH)2D3 in comparison with the synthetic sample based on the data from 1H-NMR, GC/MS, and LC/atmospheric pressure chemical ionization-MS. The conjugation position was determined to be the 24-hydroxy group by the LC/electrospray ionization-MS and -MS/MS/MS combined with derivatization. To our knowledge, this is the first reported instance of the epimerization of the 3-hydroxy group of vitamin D compound with no hydroxy group at the 1alpha-position.