We used 2,3-dichloro-N-methylmaleimide to synthesize a library of labeled α-amino acids. When necessary, the amino acids were protected to obtain standards of amino acids labeled at their side chains. Amino acid labeling was followed by the labeling of oligopeptides and, finally, the protein. The labeled amino acids and oligopeptides were spectroscopically characterized, and the resulting data were used to estimate the number of labeled amino acid residues on the surface of bovine serum albumin (BSA). In addition, the stability of 2,3-dichloro-N-methylmaleimide in aqueous buffer systems was evaluated
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