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.