3-Hydroxykynurenic acid: Physicochemical properties and fluorescence labeling

SHMIDT, MARÍA S.; GARCÍA VIOR, MARÍA C.; EZQUERRA RIEGA, SERGIO D.; LÁZARO-MARTÍNEZ, JUAN M.; ABASOLO, MARÍA I.; LAZARO-CARRILLO, ANA; TABERO, ANDREA; VILLANUEVA, ANGELES; MOGLIONI, ALBERTINA G.; BLANCO, MARÍA M.; STOCKERT, JUAN C.

DYES AND PIGMENTS

ELSEVIER SCI LTD

Año: 2019 vol. 162 p. 552 - 561

0143-7208

Some derivatives are normal metabolites, and others are used as antibacterial, antimalarial, and anticancer agents. In this work, we describe the synthesis, physicochemical properties, and fluorescence features of a new 4-quinolinone fluorophore, 3-hydroxykynurenic acid (3-HOKA). 3-HOKA was obtained by alkoxide-induced rearrangement of ethyl isatinacetate followed by acidification and then alkaline hydrolysis. The fluorescent compound was characterized by NMR, MS, IR, and UV?Vis spectra. 3-HOKA can exist under a keto-enol equilibrium, but the 4-quinolinone form is the predominant tautomer. In PBS (pH = 7.4), the anionic keto form of 3-HOKA showed a maximum absorption at 368 nm, a fluorescence peak at 474 nm, and a fluorescence quantum yield (ΦF): 0.73. 3-HOKA is photostable and is a moderately weak oxygen generator. Viability assays on HeLa cells indicated that 3-HOKA did not induce significative cytotoxic effects. Under UV excitation, a bright blue fluorescence was selectively found in a singular body within the cytoplasm, a labeling pattern that suggests the possible localization of the probe in the centriole or related structures. Therefore, this novel fluorophore represents a promising prototype compound owing to its biocompatibility and potential biological applications.