Synthesis of tritiated 1α,25-dihydroxy-22-oxavitamin D3

Synthesis of two tritiated 1α,25-dihydroxy-22-oxavitamin D 3 (OCT), [26- 3 H 3 ]OCT (3) and [2β- 3 H]OCT (4), is described. [26- 3 H 3 ]OCT (3) was prepared by tritiation at the side chain with tritiated methylmagnesium iodide and [2β- 3 H]OCT (4) was labeled at the A-ring by tritiation with sodium borotritiide.