Protein labeling with cyanobenzothiazole conjugates

A method for detecting a peptide or protein, comprising

• a) contacting a sample comprising an N-terminal cysteine labeled peptide or protein with a cyanobenzothiazole derivative of Formula I
• wherein
• Z is H, F, Cl, Br, I, CN, amino, alkylamino, dialkylamino, alkyl ester, carboxy, carboxylic acid salt, alkyl amide, phosphate, alkyl phosphonate, sulfate, alkyl sulfonate, nitro, or C1-C10 alkyl optionally unsaturated and optionally substituted with amino, hydroxy, oxo (═O), nitro, thiol, or halo;
• each R1 is independently H, F, Cl, Br, I, CN, C1-C6 alkyl, C1-C6 alkoxy, or C1-C6 alkylthio, wherein each alkyl, alkoxy, or alkylthio is optionally substituted with F, Cl, Br, I, amino, alkenyl, alkynyl, cycloalkyl, aryl,alkyl sulfonate, or CO2M wherein M is H, an organic cation, or an inorganic cation;
• n is 0, 1, or 2;
• Y is a linking group comprising C1-C16 alkyl optionally substituted with one or more halo, oxo (═O), C1-C6alkyl, or C1-C6alkoxy, and optionally interrupted with one or more N(R1), O, S, or —NH—C(═O)— groups;
• and
• X is a fluorescent dye;
• so as to yield a fluorescently-labeled peptide or protein;
• and
• b) detecting the presence or absence of fluorescence in the sample.

A method for detecting a peptide or protein, comprising:

• a) contacting a sample comprising an N-terminal cysteine labeled peptide or protein with a cyanobenzothiazole derivative of Formula I
• wherein
• Z is H, F, Cl, Br, I, CN, amino, alkylamino, dialkylamino, alkyl ester, carboxy, carboxylic acid salt, alkyl amide, phosphate, alkyl phosphonate, sulfate, alkyl sulfonate, nitro, or C1-C10 alkyl optionally unsaturated and optionally substituted with amino, hydroxy, oxo (═O), nitro, thiol, or halo;
• each R1 is independently H, F, Cl, Br, I, CN, C1-C6 alkyl, C1-C6 alkoxy, or C1-C6 alkylthio, wherein each alkyl, alkoxy, or alkylthio is optionally substituted with F, Cl, Br, I, amino, alkenyl, alkynyl, cycloalkyl, aryl,alkyl sulfonate, or CO2M wherein M is H, an organic cation, or an inorganic cation;
• n is 0, 1, or 2;
• Y is a linking group comprising C1-C16 alkyl optionally substituted with one or more halo, oxo (═O), C1-C6alkyl, or C1-C6alkoxy, and optionally interrupted with one or more N(R1), O, S, or —NH—C(═O)— groups;
• and
• X is a fluorescent dye;
• so as to yield a fluorescently-labeled peptide or protein;
• and
• b) combining the fluorescently-labeled peptide or protein with a sample comprising a second peptide or protein that interacts, or is suspected of interacting with, the fluorescently-labeled peptide or protein, wherein the interaction yields a complex;
• and
• c) detecting fluorescence in the complex.