Natural 25,26-dihydroxyvitamin D3 is an epimeric mixture.
Radiolabeled 25,26-dihydroxyvitamin D3 was prepared in vitro by using chicken kidney homogenates and in vivo in rats from [23,24-3H]-25-hydroxyvitamin D3. These compounds were mixed with synthetic (25S)- and (25R)-25,26-dihydroxyvitamin D3, converted to the corresponding (+)-alpha-methoxy-alpha-trifluoromethylphenylacetyl esters, and subjected to high-performance liquid chromatography that separates the derivatized epimers. The radiolabeled 25,26-dihydroxyvitamin D3 derivatives were a 1:1 mixture of the 25S and 25R isomers. Similarly unlabeled 25,26-dihydroxyvitamin D3 isolated from the plasma of rats given large amounts of vitamin D3 was shown to be a 1:1 mixture of the S and R isomers. Therefore, naturally occurring 25,26-dihydroxyvitamin D3 is a mixture of the 25R and 25S isomers and not just the S isomer reported previously.
D000818:Animals; D002645:Chickens; D002851:Chromatography, High Pressure Liquid; D004100:Dihydroxycholecalciferols / Q000302:isolation & purification / Q000378:metabolism*; D007536:Isomerism; D007668:Kidney / Q000378:metabolism*; D014316:Tritium
D004100:Dihydroxycholecalciferols; D014316:Tritium; C026032:25,26-dihydroxycholecalciferol