New glycoconjugation strategies for Ruthenium(II) arene complexes via phosphane ligands and assessment of their antiproliferative activity.

Glycoconjugation is a powerful tool to improve the anticancer activity of metal complexes. Herein, we modified commercial arylphosphanes with carbohydrate-derived fragments for the preparation of novel glycoconjugated ruthenium(II) p-cymene complexes. Specifically, d-galactal and d-allal-derived vinyl epoxides (VEß and VEα) were coupled with (2-hydroxyphenyl)diphenylphosphane, affording the 2,3-unsaturated glycophosphanes 1ß and 1α. Ligand exchange with [Ru(C2O4)(η6-p-cymene)(H2O)] gave the glycoconjugated complexes Ru1ß and Ru1α which were subsequently dihydroxylated with OsO4/N-methylmorpholine N-oxide to Ru2ß and Ru2α containing O-benzyl d-mannose and d-gulose units respectively. Besides, aminoethyl tetra-O-acetyl-ß-d-glucopyranoside was condensed with borane-protected (4-diphenylphosphanyl)benzoic acid by HATU/DIPEA under MW heating, to afford the amide 3∙BH3. Zemplén deacylation with MeONa/MeOH gave the deprotected d-glucopyranoside derivative 4∙BH3. The glycoconjugated phosphane complexes Ru3 and Ru4 were obtained by reaction of the phosphane-boranes 3∙BH3 and 4∙BH3 with [Ru(C2O4)(η6-p-cymene)(H2O)]. The employed synthetic strategies were devised to circumvent unwanted phosphine oxidation. The compounds were purified by silica chromatography, isolated in high yield and purity and characterized by analytical and spectroscopic (IR and multinuclear NMR) techniques. The behaviour of the six glycoconjugated Ru complexes in aqueous solutions was assessed by NMR and MS measurements. All compounds were screened for their in vitro cytotoxicity against A2780/A2780R human ovarian and MCF7 breast cancer cell lines, revealing a significant cytotoxicity for complexes containing the 2,3-unsaturated glycosyl unit (Ru1ß, Ru1α). Additional studies on five other human cancer cells, as well as time-dependent toxicity and cell-uptake analyses on ovarian cancer cells, confirmed the prominent activity of these two compounds - higher than cisplatin - and the better performance of the ß anomer. However, Ru1ß, Ru1α did not show preferential activity against cancer cells with respect to fetal lung fibroblast and human embryonic kidney cells as models of normal cells. The effects of the two ruthenium glycoconjugated compounds in A2780 ovarian cancer cells were further investigated by cell cycle analysis, induction of apoptosis, intracellular ROS production, activation of caspases 3/7 and disruption of mitochondrial membrane potential. The latter is a relevant factor in the mechanism of action of the highly cytotoxic Ru1ß, inducing cell death by apoptosis.

Stereoselective synthesis of new pyran-dioxane based polycycles from glycal derived vinyl epoxide.

Chiral heteropolycyclic structures are widespread in compounds of high pharmaceutical relevance. In particular, linear fused pyran-dioxane based polycycles can be found in several naturally occurring molecules, and among them, cardiac glycosides and antibiotic spectinomycin are characterized by a cis-cisoid-trans geometry. Then, the stereocontrol in the synthesis of this type of polycyclic scaffold is of primary importance. Herein, we present two novel linear fused pyran-dioxane based bi- and tricycles, synthesized with total stereoselectivity from a glycal derived vinyl epoxide. The straightforward methodology described involves a substrate-dependent stereospecific glycosylation step followed by an intramolecular SN2' conjugate addition process, leading to a pyran-dioxane-cyclohexane tricycle with a cis-cisoid-trans stereochemistry, in agreement with the geometry of many natural products. The stereochemical analysis of these compounds, which was realized by a combined NMR/computational approach, is also reported.

New lipophilic glycomimetic DC-SIGN ligands: Stereoselective synthesis and SPR-based binding inhibition assays.

The design and synthesis of efficient ligands for DC-SIGN is a topic of high interest, because this C-type lectin has been implicated in the early stages of many infection processes. DC-SIGN membrane-protein presents four carbohydrate-binding domains (CRD) that specifically recognize mannose and fucose. Therefore, antagonists of minimal disaccharide epitope Manα(1,2)Man, represent potentially interesting antibacterial and antiviral agents. In the recent past, we were able to develop efficient antagonists, mimics of the natural moiety, characterized by the presence of a real d-carbamannose unit which confers greater stability to enzymatic breakdown than the corresponding natural disaccharide ligand. Herein, we present the challenging stereoselective synthesis of four new amino or azide glycomimetic DC-SIGN antagonists with attractive orthogonal lipophilic substituents in C(3), C(4) or C(6) positions of the real carba unit, which were expected to establish crucial interactions with lipophilic areas of DC-SIGN CRD. The activity of the new ligands was evaluated by SPR binding inhibition assays. The interesting results obtained, allow to acquire important information about the influence of the lipophilic substituents present in specific positions of the carba scaffold. Furthermore, C(6) benzyl C(4) tosylamide pseudodisaccharide displayed a good affinity for DC-SIGN with a more favorable IC50 value than those of the previously described real carba-analogues. This study provides valuable knowledge for the implementation of further structural modifications towards improved inhibitors.

New Coumarin Dipicolinate Europium Complexes with a Rich Chemical Speciation and Tunable Luminescence.

Europium (III) luminescent chelates possess intrinsic photophysical properties that are extremely useful in a wide range of applications. The lack of examples of coumarin-based lanthanide complexes is mainly due to poor photo-sensitization attempts. However, with the appeal of using such a versatile scaffold as antenna, especially in the development of responsive molecular probes, it is worth the effort to research new structural motifs. In this work, we present a series of two new tris coumarin-dipicolinate europium (III) complexes, specifically tailored to be either a mono or a dual emitter, tuning their properties with a simple chemical modification. We also encountered a rich chemical speciation in solution, studied in detail by means of paramagnetic NMR and emission spectroscopy.

Coumarin-based fluorescent biosensor with large linear range for ratiometric measurement of intracellular pH.

Intracellular pH is a critical parameter involved in cell machinery, and its dysregulation can either cause or signal pathologic states. Currently described fluorescent pH probes are based on single acid-base equilibria, and for this reason are intrinsically unable to capture the wide range of cell pH, usually spanning over more than four units. Here we describe a fluorescent pH biosensor based on a conjugated coumarin-triazine scaffold that is excitable in the visible range, shows pseudo-linear ratiometric response over more than 6 pH units with a single fluorogenic unit, and allows imaging of the whole endo-lysosomal pH landscape of living cells with a single acquisition. The probe can discriminate, on the basis of intracellular acidity, between physiologic and tumor cells, being potentially suitable in perspective as diagnostic tool.

New 1,3-Disubstituted Benzo[h]Isoquinoline Cyclen-Based Ligand Platform: Synthesis, Eu3+ Multiphoton Sensitization and Imaging Applications.

The development of lanthanide-based luminescent probes with a long emission lifetime has the potential to revolutionize imaging-based diagnostic techniques. By a rational design strategy taking advantage of computational predictions, a novel, water-soluble Eu3+ complex from a cyclen-based ligand bearing 1,3-disubstituted benzo[h]isoquinoline arms was realized. The ligand has been obtained overcoming the lack of reactivity of position 3 of the isoquinoline moiety. Notably, steric hindrance of the heteroaromatic chromophore allowed selective and stoichiometry-controlled insertion of two or three antennas on the cyclen platform without any protection strategy. The complex bears a fourth heptanoic arm for easy conjugation to biomolecules. This new chromophore allowed the sensitization of the metal center either with one or two photons excitation. The suitability as a luminescent bioprobe was validated by imaging BMI1 oncomarker in lung carcinoma cells following an established immunofluorescence approach. The use of a conventional epifluorescence microscope equipped with a linear structured illumination module disclosed a simple and inexpensive way to image confocally Ln-bioprobes by single photon excitation in the 350-400 nm window, where ordinary confocal systems have no excitation sources.

Synthesis and Biological Evaluation of New Glycoconjugated LDH Inhibitors as Anticancer Agents.

Conjugation of known biologically active molecules to carbohydrate frameworks represents a valuable option for the preparation of hybrid, structurally-related families of compounds with the aim of modulating their biological response. Therefore, we present here a study on the preparation of d-galacto, d-manno, d-gluco, and d-lactose glycoconjugates of an established N-hydroxyindole-based (NHI) inhibitor of lactated dehydrogenase (LDH). Structural variations involved the sugar stereochemistry and size as well as the anchoring point of the NHI on the carbohydrate frame (either C-1 or C-6). In the case of the galactose anomeric glycoconjugate (C-1), intriguing solvent-dependent effects were observed in the glycosylation stereochemical outcome. The biological activity of the deprotected glycoconjugates in contrasting lactate formation and cancer cell proliferation are described.

Tethering Carbohydrates to the Vinyliminium Ligand of Antiproliferative Organometallic Diiron Complexes.

Four propargyl O-glycosides derivatized with mannose, glucose, and fructose moieties were synthesized and then incorporated within a diiron structure as part of a vinyliminium ligand. Hence, six glycoconjugated diiron complexes, [2-5]CF3SO3 (see Scheme 1) and the nonglycosylated analogues [6a-b]CF3SO3, were obtained in high yields and unambiguously characterized by elemental analysis, mass spectrometry, and IR and multinuclear NMR spectroscopies. All compounds exhibited a significant stability in DMSO-d 6/D2O solution, with 63-89% of the complexes unaltered after 72 h at 37 °C and also in the cell culture medium. The cytotoxicity of [2-6]CF3SO3, as well as that of previously reported 7 and 8, was assessed on CT26 (mouse colon carcinoma), U87 (human glioblastoma), MCF-7 (human breast adenocarcinoma), and RPE-1 (human normal retina pigmented epithelium) cell lines. In general, the IC50 values correlate with the hydrophobicity of the compounds (measured as octanol-water partition coefficients) and do not show an appreciable level of selectivity against cancer cells with respect to the nontumor ones.

Functionalized aliphatic polyketones with germicide activity.

The COVID-19 pandemic has further confirmed to the community that direct contact with contaminated surfaces and objects represents an important source of pathogen spreading among humans. Therefore, it is of paramount importance to design effective germicidal paints to ensure a rapid and potent disinfectant action of surfaces. In this work, we design novel germicide polymeric coatings by inserting quaternary ammonium and sugar groups on the macromolecular backbone, thus respectively endowing the polymer with germicide features and hydrophilicity to interact with the surfaces. An aliphatic polyketone was selected as a starting polymer matrix that was functionalized with primary amine derivatives via the Paal-Knorr reaction. The resulting polymers were deposited on cellulose filter papers and checkboard charts with excellent coating yield and substrate coverage as determined by scanning electron microscopy for cellulose. Remarkably, the substrates coated by the functional polymers bearing quaternary ammonium compounds showed excellent bactericide properties with antibacterial rate of 99% and logarithmic reduction of >3. Notably, the polymers with higher hydrophobicity showed better retention on the substrate after being treated with water at neutral pH.

Glycoconjugated Metal Complexes as Cancer Diagnostic and Therapeutic Agents.

The possibility of selectively delivering metal complexes to a defined cohort of cells on the basis of their metabolic features is a highly challenging goal, which may be extremely useful for a series of purposes, including diagnosis and therapy of pathological states, such as cancer. Tumor cells display augmented requests for carbohydrates and, in particular, for glucose in order to sustain their high proliferation rate, which causes an increased glycolytic process (Warburg effect). Since several metal complexes display diagnostic and/or therapeutic properties, their conjugation to carbohydrate portions often induce their preferential accumulation in cancer cells, similarly to what is observed with fluorodeoxyglucose (FDG). In this review we have considered the latest developments of glycoconjugates containing metal complexes in their structures. These compounds are classified as diagnostic or therapeutic agents and are further systematically discussed on the basis of the metal atom they contain. Several diagnostic techniques are possible with these probes, since, depending on the metal species included in their structures, they may be employed in nuclear medicine (PET, SPECT), magnetic resonance imaging, luminescence and phosphorescence. At the same time, the lack of selective cytotoxicity displayed by several metal-based chemotherapeutic agents, may also be solved by the conjugation of these agents to carbohydrate portions. Overall, data so far available reveal the great potential of this chemical class in the early detection and in the cure of severe neoplastic diseases, which still needs to be fully explored in the clinic.