Dehydroalanine is a synthetic precursor to a wide array of protein modifications. We describe multiple methods for the chemical conversion of cysteine to dehydroalanine on peptides and proteins. The scope and limitations of these methods were investigated with attention paid to side reactions, scale, and aqueous- and bio-compatibility. The most general method investigated - a bis-alkylation-elimination of cysteine to dehydroalanine - was applied successfully to multiple proteins and enabled the site-selective synthesis of a glycosylated antibody. © The Royal Society of Chemistry 2011.