Radiolabeling of proteins with radioisotopes of copper using p‐carboxyalkylphenylglyoxal bis‐(4N‐methylthiosemicarbazone) (TSC) bifunctional chelates

A series of p-carboxyalkylphenylglyoxal and p-carboxyalkyl-1,2-diketo-bis-(N4-methylthiosemicarbazone) bifunctional ligands (TSC) have been prepared and evaluated for use in binding radioisotopes of copper to antibodies. We have developed an improved synthesis of the requisite α-ketoaldehyde and 1,2-diketone substrates used for derivatization to the bis-TSC bifunctional chelates. This approach utilizes a modified Kornblum method and provides a simple alternative to the usual method for fabrication of the 1,2-bis-TSC ligands, which avoids the use of highly toxic selenium dioxide for oxidation of substituted acetophenones to 1,2 dicarbonyl compounds. The overall yields of the bis-TSC chelates using this procedure were 8-60%. The effects of the alkyl chain length and substitution on the C-2 position on p-carboxyalkylphenyl-1,2-diketo bis-TSC bifunctional chelate for attaching radioisotopes of copper to proteins were studied. Following complexing copper-64 or copper-67 to the bis-TSC chelate, the acid moiety of the TSC chelate was activated as the tetrafluorophenyl ester. The copper-labeled activated TSC chelate was attached to bovine serum albumin under mild conditions in 3% to 40% yield. These studies have demonstrated that the shorter chain analogues of the TSC chelates from the 1,2-diketones give the highest radiolabeling yields.