New cell-penetrating fluorescent probes for cell delivery and imaging

Visualization of specific intracellular biological activities plays a key role in the understanding of cells behavior; therefore the development of new probes and sensors become more and more important in recent decades. Despite the growing utility of small-molecule fluorophores and a wide variety of fluorescent probes, only few of them are capable of penetrating spontaneously into the cell, thus chemical sensors are usually composed of a recognition unit, a cell penetrating unit and a fluorescent unit. In our laboratory we developed novel organic fluorescent probes consisting of chimeric new cell permeable fluorophores having remarkable delivery abilities, and recognition units usually peptide sequences.

The fluorophores represent the derivatives of natural products having hexa-substituted benzene obtained by MCR4. Their synthesis is based on the new multicomponent reaction recently developed in our laboratory: the reaction of substituted chiral tetramic acids which together with an aldehyde, an iso-cyanide, a dienophile and a Lewis acid; produce 3-substituted iso-indolinones in one pot¹.

Non toxic analogs have good fluorescence profiles, similar to well-known molecular probes, and they are taken up by cells few seconds after incubation. Together, these qualities make them good candidates for bio-sensing , targeting and imaging applications.

The proposed new methodology is based in the synthesis of the fluorescent unit directly on a peptide targeting unit in solid phase at the end of the peptide synthesis. A proof of concept is accomplished by the synthesis of a d-[KLAKLAK]₂ probe known as being cell toxic via mitochondria disruption but unable to penetrate itself into the cell.

References

(1)Gelman, M; Massarano, T.; Lavi, R.; Byk, G. A New Multicomponent Reaction MCR4 for the Synthesis of Analogs of Staurosporine. Curr. Org. Chem. 2018, 22, 505-517.