Synthesis, structural study and antitumor activity of novel alditol-based imidazophenanthrolines (aldo-IPs).

A series of 1H-imidazo [4,5-f][1,10] phenanthroline derivatives functionalized at 2-position with chiral, and conformationally flexible polyhydroxy alkyl chains derived from carbohydrates (alditol-based imidazophenanthrolines, aldo-IPs) is presented herein. These novel glycomimetics showed relevant and differential cytotoxic activity against several cultured tumor cell lines (PC3, HeLa and HT-29), dependent on the nature and stereochemistry of the polyhydroxy alkyl chain. The mannose-based aldo-IP demonstrated the higher cytotoxicity in the series, substantially better than cisplatin metallo-drug in all cell lines tested, and better than G-quadruplex ligand 360A in HeLa and HT29 cells. Cell cycle experiments and Annexin V-PI assays revealed that aldo-IPs induce apoptosis in HeLa cells. Initial study of DNA interactions by DNA FRET melting assays proved that the aldo-IPs produce only a slight thermal stabilization of DNA secondary structures, more pronounced in the case of quadruplex DNA. Viscosity titrations with CT dsDNA suggest that the compounds behave as DNA groove binders, whereas equilibrium dialysis assays showed that the compounds bind CT with Ka values in the range 104-105 M-1. The aldo-IP derivatives were obtained with synthetically useful yields through a feasible one-pot multistep process, by aerobic oxidative cyclization of 1,10-phenanthroline-5,6-diamine with a selection of unprotected aldoses using (NH4)2SO4 as promoter.

Carbohydrate effect of novel arene Ru(II) phenanthroline-glycoconjugates on metastatic biological processes.

Novel water-soluble half-sandwich ruthenium(II) polypyridyl-glycoconjugates [Ru(p-cymene)Cl{N-(1,10-phenanthroline-5-yl)-ß-glycopyranosylamine}][Cl] (glycopyranosyl = d-glucopyranosyl (1), D-mannopyranosyl (2), L-rhamnopyranosyl (3) and l-xylopyranosyl (4)) have been synthesized and fully characterized. Their behaviour in water under physiological conditions has been studied by nuclear magnetic resonance spectroscopy, revealing their hydrolytic stability. Interactions of the novel compounds with duplex-deoxiribonucleic acid (dsDNA) were investigated by different techniques and the results indicate that, under physiological pH and saline conditions, the metal glycoconjugates bind DNA in the minor groove and/or through external, electrostatic interactions, and by a non-classical, partial intercalation mechanism in non-saline phosphate buffered solution. Effects of compounds 1-4 on cell viability have been assessed in vitro against two human cell lines (androgen-independent prostate cancer PC-3 and non-tumorigenic prostate RWPE-1), showing moderate cytotoxicities, with IC50 values higher than those found for free ligands [N-(1,10-phenanthroline-5-yl)-ß-glycopyranosylamine] (glycopyranosyl = d-glucopyranosyl (a), D-mannopyranosyl (b), L-rhamnopyranosyl (c) and l-xylopyranosyl (d)) or corresponding metal-aglycone. Cell viability was assayed in the presence and absence of the glucose transporters (GLUTs) inhibitor [N4-{1-(4-cyanobenzyl)-5-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl}-7-fluoroquinoline-2,4-dicarboxamide] (BAY-876), and the results point to a negligible impact of the inhibition of GLUTs on the cytotoxicity caused by Ru(II) compounds 1-4. Remarkably, glycoconjugates 1-4 potently affect the migration pattern of PC-3 cells, and the wound healing assay evidence that the presence of the carbohydrate and the Ru(II) center is a requisite for the anti-migratory activity observed in these novel derivatives. In addition, derivatives 1-4 strongly affect the matrix metalloproteinase MMP-9 activities of PC-3 cells, while proMMP-2 and especially proMMP-9 were influenced to a much lesser extent.

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).

Experimental observations on the reductive cleavage of endo and exo 3,4-O-benzylidene fucopyranoside derivatives.

Reductive cleavage of methyl 3,4-O-benzylidene-α-L-fucopyranosides with BH3·THF-TfOH and NaCNBH3-TfOH systems resulted in enhanced reaction rates and selectivity compared to BH3·THF-Bu2BOTf. With this latter system, the nature of the O-2 substituent exerted a clear control on the reactivity but practically did not affect the regioselectivity. With TfOH the direction of cleavage was determined, as expected, by the configuration of the acetal carbon atom, but slightly influenced by its competitive epimerization. Protic conditions provided higher regioselectivity in the openings of the exo isomers, affording a useful approach to the practical synthesis of 3-O-benzyl ethers.

4,5-Diazafluorene N-glycopyranosyl hydrazones as scaffolds for potential bioactive metallo-organic compounds: Synthesis, structural study and cytotoxic activity.

A series of novel N1-(4,5-diazafluoren-9-yliden)-N2-glycopyranosyl hydrazines was prepared in synthetically useful yields by treatment of 9H-4,5-diazafluoren-9-hydrazone with different unprotected monosaccharides. The reactions with the monosaccharides tested afforded stereoselectively, and exclusively, cyclic derivatives, whose structures correspond to N-ß-glycopyranosyl hydrazones except for the d-arabinose derivative that agrees with the α-anomer. Several copper(II) complexes having a 2:1 ligand to metal mole ratio were also prepared. The metal complexes can bind DNA sequences and preferentially stabilize G-quadruplex DNA structures over dsDNA. The fucose, rhamnose and deoxyglucose copper(II) complexes exhibited a cytotoxic activity against cultured HeLa and PC3 tumor cells comparable to other metal complexes normally used for chemotherapeutic purposes, such as cisplatin.

Human telomeric G-quadruplex DNA interactions of N-phenanthroline glycosylamine copper(II) complexes.

We report in this article the interactions of five N-(1,10-phenanthrolin-5-yl)-ß-glycopyranosylamine copper(II) complexes with G-quadruplex DNA. Specifically, the interactions of these compounds with a human telomeric oligonucleotide have been assessed by fluorescence-based assays (FRET melting and G4-FID), circular dichroism and competitive equilibrium dialysis experiments. The metal complexes bind and stabilize G-quadruplex DNA structures with apparent association constants in the order of 10(4)-10(5)M(-1) and the affinity observed is dependent on the ionic conditions utilized and the specific nature of the carbohydrate moiety tethered to the 1,10-phenanthroline system. The compounds showed only a slight preference to bind G-quadruplex DNA over duplex DNA when the quadruplex DNA was folded in sodium ionic conditions. However, the binding affinity and selectivity, although modest, were notably increased when the G-quadruplex DNA was folded in the presence of potassium metal ions. Moreover, the study points towards a significant contribution of groove and/or loop binding in the recognition mode of quadruplex structures by these non-classical quadruplex ligands. The results reported herein highlight the potential and the versatility of carbohydrate bis-phenanthroline metal-complex conjugates to recognize G-quadruplex DNA structures.