title: Unique rearrangement of ergocalciferol side chain in vitro: production of a biologically highly active homologue of 1,25-dihydroxyvitamin D3.
abstract: In vitro incubation of 24-epi-25-hydroxyvitamin D2 with chicken kidney homogenate produced several compounds, one of which had an affinity equal to that of 1,25-dihydroxyvitamin D2 for the chick intestinal receptor. The affinity of 24-epi-1,25-dihydroxyvitamin D2 for the same receptor was found to be half that of 1,25-dihydroxyvitamin D2. The unknown compound was produced only when homogenate was prepared from pooled kidneys taken from both vitamin D deficient and replete chickens. The compound has been tentatively identified as 1,25-dihydroxy-22-dehydro-26-homovitamin D3 by ultraviolet absorption spectrophotometry and mass spectrometry. Chemical synthesis of 1,25-dihydroxy-22-dehydro-26-homovitamin D3 provided additional evidence for the structure. Administration of this 26-homologue of 1,25-dihydroxyvitamin D3 at the dose level of 650 pmol/rat stimulated bone calcium mobilization in the hypocalcemic rat equal to that of 1,25-dihydroxyvitamin D3. Thus, this paper demonstrates unique methyl migration on the side chain of 24-epi-1,25-dihydroxyvitamin D3 to form a more biologically potent analogue.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000302:isolation & purification; D002645:Chickens; D004872:Ergocalciferols / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: D004872:Ergocalciferols; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; C087590:22-dehydro-1,25-dihydroxy-24-homovitamin D3; D002117:Calcitriol