Fluorescent labeling of living cells

A compound of Formula I:

• wherein:
• B at each occurrence is independently —CH2OC(O)CH3 or a group of Formula II:
• Y1 and Y2 are independently O or NR6;
• R1, R2, R3, R4, and R5 at each occurrence are independently substituted or unsubstituted C1 to C8 alkyl;
• R6 at each occurrence is independently H or substituted or unsubstituted C1 to C8 alkyl;
• R7, R8, R9, R10, R11, R12, R13, R14, R15, R16 are independently H, substituted or unsubstituted C1 to C8 alkyl, substituted or unsubstituted C6 to C14 aryl, substituted or unsubstituted C1 to C8 alkoxy, substituted or unsubstituted C6 to C14 aryloxy, hydroxy, halo, nitro, nitrile, amino, amido, imido, urea, amidine, guanidine, enamine, urethane, oxime, hydroxylamine, carboxyl, ester, oxo, thiol, sulfide, sulfoxide, sulfone, sulfonyl, sulfonate, sulfonamide, hydrazine, hydrazide, hydrazone, azide, cyanate, isocyanate, thiocyanate, or isothiocyanate;
• and
• one of R13, R14, R15 or R16 is a group of Formula III:
• wherein:
• L is a linker selected from the group consisting of substituted or unsubstituted C1 to C30 alkylene and substituted or unsubstituted C1 to C30 heteroalkylene, or is an amino acid linker comprising from 1 to about 20 amino acids;
• and
• P is a polypeptide comprising a C-terminus and an N-terminus, wherein the C-terminus of the polypeptide is bonded to the NH2 moiety, and wherein P is cleavable by a sortase enzyme.