Technetium-99m-labeled phosphonic acid analog of serine: bone uptake

A phosphonic acid analog of serine (PAAS), its P-methyl derivative, and an allied compound were labeled with 99mTc, and evaluated in experimental animals. These molecules were able to bind 99mTc in the presence of stannous ions, but the biologic behavior of the later two labeled compounds was quite different from that of the first one. Technetium-99m-labeled PAAS behaved like 99mTc-labeled methylene diphosphonate, but its P-methyl derivative and the third agent showed little bone accumulation. It appears that both hydroxyl groups attached to the phosphorus atom are essential for uptake in bone, but that only one is required for binding 99mTc.