Dextran was applied for the design of biopolymers bearing reactive C-C double bond for subsequent "click" reaction with thiols. The polysaccharide was functionalized with maleimido- and norbornene moieties as "ene" compound for thiol-Michael and radical thiol-ene reaction, respectively. The hydroxyl groups of dextran were esterified with 6-maleimidohexanoic acid or 5-norbornene-2-carboxylic acid in an efficient, homogeneous one-step synthesis applying different in-situ activation methods of the carboxylic acids. The water- or organo-soluble dextran derivatives obtained were allowed to react with N-acetyl-L-cysteine to study the reactivity of the ene-functionalized derivatives in thiol-ene "click" reactions dependent on solvent, reaction time, and activation/initiation reagent. The dextran esters and the corresponding N-acetyl-L-cysteine adducts were characterized by means of elemental analysis, NMR-, and FT-IR spectroscopy.