wherein R12═C1-3-alkyl, the wavy line indicates the connection to the remainder of the cytotoxin, and wherein D is conjugated to (L4)q by replacing the amine H atom, and to conjugates obtainable by reacting the compound according to the invention with a protein comprising a click probe F capable of reacting with click probe Q in a click reaction. The invention further relates to a bioconjugate according to general structure (2): Pr-[(L6)-Z-(L1)n-(L2)o-(L3)p-(L4)q-D]xx (2), wherein Z is a connecting group that is formed in a click reaction, L6 is a linker that links Z to Pr and Pr is a (glyco)protein.
