Unusual substrates of tubulin tyrosine ligase

A method for the production of a functionalized polypeptide comprising

• (a) introducing or adding at the C-terminus of a polypeptide a recognition sequence for tubulin tyrosine ligase;
• (b) contacting the polypeptide obtained in step (a) in the presence of tubulin tyrosine ligase and a compound under conditions suitable for the tubulin tyrosine ligase to functionalize said polypeptide with said compound, wherein said compound having a structure according to Formula I
• wherein
• X is O, NR1 or S;
• Y is selected from the group consisting of hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroarylalkyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heteroalkenyl and substituted or unsubstituted heteroalkynyl;
• Z is selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, substituted or unsubstituted arylalkyl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroarylalkyl, substituted or unsubstituted heterocyclyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heteroalkenyl and substituted or unsubstituted heteroalkynyl;
• and
• R1 is selected from the group consisting of hydrogen, substituted or unsubstituted (C1-C6)alkyl, substituted or unsubstituted (C2-C6)alkenyl, substituted or unsubstituted (C2-C6)alkynyl, substituted or unsubstituted (C3-C8)cycloalkyl, substituted or unsubstituted (C6-C14)aryl and substituted or unsubstituted (C3-C14)heteroaryl;
• with the proviso that Z is not a substituted or unsubstituted monocyclic six-membered aryl.