Carbostyril Derivatives as Antenna Molecules for Luminescent Lanthanide Chelates

Luminescent lanthanide complexes consisting of a lanthanide-binding chelate and organic-based antenna molecule have unusual emission properties, including millisecond excited state lifetimes and sharply spiked spectra, compared to standard organic fluorophores. We have previously used carbostyril (cs124, 7-amino-4-methyl-2(1H)-quinolinone) as an antenna molecule (Li and Selvin, J. Am. Chem. Soc., 1995) attached to a polyaminocarboxylate chelate such as DTPA. Here, we report the chelate syntheses of DTPA conjugated with cs124 derivatives substituted on the 1-, 3-, 4-, 5-, 6-, and 8-position. Among them, the DTPA chelate of cs124-6-SO3H has similar lifetime and brightness for both Tb^3+ and Eu^3+ compared to the corresponding DTPA-cs124 complexes, yet it is significantly more soluble in water. The Tb^3+ complex of DTPA-cs124-8-CH3 has significantly longer lifetime compared to DTPA-cs124 (1.74 vs 1.5 ms), indicating higher lanthanide quantum yield resulting from the elimination of back emission energy transfer from Tb^3+ to the antenna molecule. Thiol-reactive forms of chelates were made for coupling to proteins. These lanthanide complexes are anticipated to be useful in a variety of fluorescence-based bioassays.