Abstract: A bicyclic, non-aromatic hydrocarbon compound, optionally having one or more N, O or S atoms in the bicyclic skeleton, and having as substituents an acid group and an amido group, which are vicinal and in a syn-position, wherein the amido group is not anilido and the acid group is carboxyl or carboxyl in a form metabolizable to a free carboxyl group, and wherein said bicyclic skeleton is optionally unsaturated, except in the bond between said groups, acid-cleavably links an amide-containing active agent to a targeting agent, which is linked by a linker arm to the bicyclic skeleton.