Stereoselective synthesis of (25)-25,26-dihydroxy-23-oxovitamin D3 and its enzymatic conversion to (25)-1α,25,26-trihydroxy-23-oxovitamin D3, a putative metabolite of vitamin D3

(25 R )-25,26-Dihydroxy-23-oxovitamin D 3 was synthesized efficiently and stereoselectively, and it was converted enzymatically to (25 R )-1α,25,26-trihydroxy-23-oxovitamin D 3 , a putative metabolite of 1α,25-dihydroxyvitamin D 3 . The spectral and chemical properties of (25 R )-25,26-dihydroxy-23-oxovitamin D 3 and its 1α,hydroxylated derivative disagree with those reported for the isolated metabolite.