Bisphosphonic compounds. I. Preparation of 13 C‐ and 14 C‐labelled clodronate

Tetrakis(1‐methylethyl) (methylene‐ 13 C)bisphosphonate was obtained from 13 C‐methyliodide via the Michaelis‐Arbuzov reaction with tris(1‐methylethyl)phosphite followed by condensation with chlorophosphonic acid bis(1‐methylethyl)ester. Tetrakis(1‐methylethyl) (methylene‐ 14 C)bisphosphonate was prepared from 14 C‐dibromomethane via the Michaelis‐Arbuzov reaction with excess of tris(1‐methylethyl)phosphite. Both of these labelled tetraesters were chlorinated with NaOCl, hydrolysed with HCl and neutralized with NaOH similarly. The overall yield of 13 C‐clodronate, (dichloromethyl one‐ 13 C)bisphosphonic acid disodium salt tetrahydrate, was 71% with 99.5% isotopic and 99.8% chemical purity. The overall radiochemical yield of 14 C‐clodronate was 9.8%.