Abstract: The present invention relates to a prodrug or a pharmaceutically acceptable salt thereof comprising a drug linker conjugate D-L, wherein -D is an amine containing biologically active moiety; and -L is a non-biologically active linker moiety -L1 represented by formula (I): wherein the dashed line indicates the attachment to the amine of the biologically active moiety and wherein R1, R1a, R2, R2a, R3, R3a, X, X1, X2, X3 have the meaning as indicated in the description and the claims and wherein L1 is substituted with one to four groups L2-Z and optionally further substituted, provided that the hydrogen marked with the asterisk in formula (I) is not replaced by a substituent; wherein L2 is a single chemical bond or a spacer; and Z is a carrier group. The invention also relates to A-L, wherein A is a leaving group, pharmaceutical composition comprising said prodrugs and their use as medicaments.