The invention relates to starch derivatives of formula (I), in which: X represents a bromine or iodine atom; R'' represents a straight-chain or branched alkyl group, aryl group or aralkyl group, and; R--CO-- represents an oxidized substituted or unsubstituted starch radical that is oxidized on the reducing terminal group to form a carboxylic acid. Starch derivatives of formula (I) can selectively couple to active substances containing SH groups and have a prolonged half-life period in the human body. The invention also relates to coupling products of compound (I) with active substances, to methods for the production thereof, and to their use as medicaments ##STR00001##