DBCO-Maleimide is a sulfhydryl reactive reagent containing a maleimide group and a DBCO moiety. Maleimide group specifically and efficiently reacts with thiols to form thioether bonds. The low mass weight will add minimal spacer to modified molecules and will enable simple and efficient incorporation of DBCO moiety into cysteine-containing peptides or other thiol-containing biomolecules. DBCO is commonly used for copper-free Click Chemistry reactions.