Design and synthesis of sulfur-35 agents and their applications for protein labeling

Two new 35S reagents were developed to radiolabel proteins. The first reagent, N-succinimidyl-4-(methane [35S]sulfonylamino-methyl)-benzoate (SMSB), acylates the e-amino group of lysine residues in proteins. The second reagent, 4-(methane [35S]sulfonylamino-methyl)-phenylpropylaldehyde (MSAPPA), labels lysine residues via reductive alkylation. Comparing the two methods, the reductive alkylation method labeled proteins over a broader pH range with higher overall radiochemical yield. More than ten monoclonal antibodies (mAbs) have been labeled with these 35S labeling reagents, the biological activity of the mAbs was unchanged. Part of this work was presented in the Ninth International Symposium on the Synthesis and Applications of Isotopically Labelled Compounds, Edinburgh, 16–20 July 2006. Copyright © 2009 John Wiley & Sons, Ltd.