Chemical synthesis, biological activity, and metabolism of 25-hydroxy-24-oxovitamin D3

25-Hydroxy-24-oxovitamin D3 (25(OH)24-oxo-D3), a metabolite of 25-hydroxyvitamin D3, has been chemically synthesized. The ultraviolet, mass, infrared, and proton nuclear magnetic resonance spectra of the 25(OH)24-oxo-D3 were identical with those of the natural product isolated from chick kidney incubates. The oxo compound showed biological activity similar to 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) in vitamin D-deficient chicks in enhancing intestinal calcium transport and bone calcium mobilization activities. Although 25(OH)24-oxo-D3 partially restored the impaired eggshell weights of Japanese quails fed a vitamin D-deficient diet, it was much less potent than 25-hydroxyvitamin D3 or 1 alpha, 25-dihydroxyvitamin D3. In addition, there was no effect on the calcification of medullary bone. When 25(OH)24-oxo[3H]D3 was incubated with kidney homogenates from vitamin D-deficient chicks, it was metabolized to [3H]1 alpha, 24,25-trihydroxyvitamin D3 and a metabolite which was eluted in a region between authentic 24R,25(OH)2D3 and 1 alpha, 25-dihydroxyvitamin D3 on high pressure liquid chromatography. In the incubates of kidney homogenates from vitamin D-supplemented chicks, those metabolites were not detected. In vitamin D-supplemented chicks, the recovery of radioactivity in the chloroform phase extracted by the method of Bligh and Dyer was only 50%, while that in vitamin D-deficient chicks was 87%. Moreover, the radioactivity eluted in the 25(OH)24-oxo-D3 fraction from vitamin D-supplemented chicks was only one-fifth of that from vitamin D-deficient birds. The present results indicate that the 24-oxidation of 24,25(OH)2D3 may be a route of inactivation of vitamin D3.