Guanine derivatives as substrates for O6-alkylguanine-DNA alkyltransferase and their use in labeling the enzyme and fusion proteins

O6-substituted guanine derivs. are described for use as substrates for O6-alkylguanine-DNA alkyltransferases (AGT) that can be used to label the enzyme or fusion proteins contg. it. Proteins of interest are incorporated into an AGT fusion protein, the AGT fusion protein is contacted with particular AGT substrates carrying a label, and the AGT fusion protein is detected and optionally further manipulated using the label in a system designed for recognizing and/or handling the label. The particular AGT substrates used in the method of the invention are O6-substituted guanine derivs. or related nitrogen contg. hydroxy-heterocycles and their sulfur analogs wherein the O6-substituent is an activated Me deriv. suitable for transfer from guanine or the corresponding heterocycle to AGT, and further carrying a label or a plurality of same or different labels. The invention relates also to the novel AGT substrates as such, to methods of manuf. of such novel substrates, and to intermediates useful in the synthesis of such novel AGT substrates. [on SciFinder (R)]