1. A prodrug or a pharmaceutically acceptable salt thereof, comprising a conjugate of a drug-linker DL, where-D is a nitrogen containing biologically active moiety and-L is a fragment of a biologically inactive linker - L, represented the formula (I) wherein the dotted line indicates the attachment to the nitrogen of the biologically active moiety by forming an amide bond X represents C (RR), N (R), O, C (RR ) -C (RR), C (RR) -C (RR), C (RR) -N (R), N (R) -C (RR), C (RR) -O or OC (RR) X b is C or S (O) X b is C (R, R) or C (R, R) - (R, R) X b is O, S or N-CN R, R, R, R, R, R, R, R, R, R, R, R, R, R, are independently selected from the group consisting of H and Ci ^ alkyl optionally, one or more pairs of R / R, R / R, R / R, R / Robrazuyut bond, if necessary, one or more pairs of R / R, R / R, R / R, R / R, R / R, R / Rvmeste with the atom to which they are attached, combine to form a cycloalkyl or 4-7 membered heterocyclyl, optionally, one or more pairs of R / R, R / R, R / R, R / R, R / R, R / R, R / Rvmeste with the atoms to which they are attached are connected to form a ring And, if necessary, R / Rvmeste with the nitrogen atom to which they are attached, combine to form a 4-7 membered heterocyclic ring A is selected from the group consisting of phenyl, naphthyl, indenyl, indanyl, tetralinyl, cycloalkyl, 4-7- membered heterocycle and 9-11 membered heterobicycle and wherein Lzameschen LZ 1-4 groups and optionally further substituted, provided that the hydrogen marked with the symbol * in formula (I), can be substituted with a substituent gdeLpredstavlyaet a single bond or a spacer iZ is a group-nositel.2. The prodrug of claim. 1, wherein X b is O.3. Etc
