Thiol-reactive luminescent chelates of terbium and europium.

Thiol-reactive lanthanide complexes have been synthesized that are luminescent when bound to terbium and/or europium. The complexes consist of a diethylenetriaminepentaacetate (DTPA) chelate covalently joined through one amide bond to a chromophore, carbostyril 124, and via a second amide bond to a maleimide, bromoacetamide, or pyridyldithio moiety. Site-specific attachment and characterization of the complexes attached to DNA-activating protein NtrC, to various sites on myosin, or to DNA are presented. The compounds coordinate a surprisingly large number of ligation sites of terbium when a hydrazide spacer is used between the chelate and thiol-reactive moiety, although this extra ligation can cause quenching when europium is used. Synthesis is a simple two- or three-step reaction, and purification is straightforward. The compounds should be useful as nonisotopic replacements, as long-lifetime probes in imaging, and as donors in luminescence resonance energy transfer. They are examples of a wide class of chelates that can be made conjugatable via readily available hetero- or homo-bifunctional linkers.