1H-imidazo[4,5-f][1,10]phenanthroline carbohydrate conjugates: Synthesis, DNA interactions and cytotoxic activity.

Here we present a novel family of carbohydrate conjugates based on the 2-aryl-imidazo[4,5-f][1,10]phenanthroline core modified with carbohydrates (carb-APIPs). The hybrid compounds were prepared by direct treatment of the unprotected carbohydrate with 2-(4-aminophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (APIP). The N-glycosylation reactions with the monosaccharides tested afforded stereoselectively the more stable N-ß-glycopyranosylamines that, in solution, underwent a dynamic equilibrium leading to anomeric mixtures with a small participation of the α isomer. DNA interaction experiments with telomeric G-quadruplex DNA included DNA FRET melting assays, circular dichroism, and equilibrium dialysis and revealed that the novel carb-APIPs bind the G-quadruplex structure with high affinity. Interestingly, the presence of the carbohydrate confers good selectivity towards the telomeric quadruplex structure, as suggested by competition DNA FRET melting assays. Besides the extended aromatic surface that allows π-stacking interactions, the carbohydrate part of the conjugate may contribute to groove binding recognition, as indicated by viscosity experiments. In addition, the novel carb-APIPs showed significant cytotoxic properties in PC3 and HeLa cells and, to a lesser extent, in MCF7 cells and normal human fibroblasts (HFF1).

PhenQE8, a Novel Ligand of the Human Telomeric Quadruplex.

A novel quadruplex ligand based on 1,10-phenanthroline and incorporating two guanyl hydrazone functionalities, PhenQE8, is reported herein. Synthetic access was gained in a two-step procedure with an overall yield of 61%. X-ray diffraction studies revealed that PhenQE8 can adopt an extended conformation that may be optimal to favor recognition of quadruplex DNA. DNA interactions with polymorphic G-quadruplex telomeric structures were studied by different techniques, such as Fluorescence resonance energy transfer (FRET) DNA melting assays, circular dichroism and equilibrium dialysis. Our results reveal that the novel ligand PhenQE8 can efficiently recognize the hybrid quadruplex structures of the human telomeric DNA, with high binding affinity and quadruplex/duplex selectivity. Moreover, the compound shows significant cytotoxic activity against a selected panel of cultured tumor cells (PC-3, HeLa and MCF-7), whereas its cytotoxicity is considerably lower in healthy human cells (HFF-1 and RPWE-1).