Red fluorescent dyes are usually charged, lypophilic molecules with the relatively high molecular weight, which tend to localize in specific intracellular locations, e.g., a cyanine dye Cy5 is biased towards mitochondria. They are often used as markers of biomolecules including nucleic acids and proteins. Since molecular weight of the dyes is much smaller than that of the biomolecules, the labelling has a negligible effect on the properties of the biomolecules. In contrast, conjugation of the dyes to low molecular weight (pro)drugs can dramatically alter their properties. For example, conjugates of Cy5 with lysosome‐targeting aminoferrocenes accumulate in mitochondria and exhibit no intracellular effects characteristic for the parent (pro)drugs. Herein we tested several neutral and negatively charged dyes for labelling lysosome‐targeting aminoferrocenes 7 and 8 as well as a non‐targeted control 3. We found that a BODIPY derivative BDP‐TR exhibits the desired unbiased properties: the conjugation does not disturb the intracellular localization of the (pro)drugs, their mode of action and cancer cell specificity. We used the conjugates to clarify the mechanism of action of the aminoferrocenes. In particular, we identified new intermediates, explained why lysosome targeting aminoferrocenes are more potent than their non‐targeted counterparts and evaluated their distribution in vivo.

The amount of unfolded proteins is increased in cancer cells, leading to endoplasmic reticulum (ER) stress. Therefore, cancer cells are sensitive to drugs capable of further enhancing ER stress. Examples of such drugs include the clinically approved proteosome inhibitors bortezomib and carfilzomib. Unfortunately, the known ER stress inducers exhibit dose-limiting side effects that justify the search for better, more cancer-specific drugs of this type. Herein, we report on FeC 2, which binds to unfolded proteins prevents their further processing, thereby leading to ER stress and ROS increase in cancer cells, but not in normal cells. FeC 2 exhibits low micromolar toxicity toward human acute promyelocytic leukemia HL-60, Burkitt's lymphoma BL-2, T-cell leukemia Jurkat, ovarian carcinoma A2780, lung cancer SK-MES-1, and murine lung cancer LLC1 cells. Due to the cancer-specific mode of action, 2 is not toxic in vivo up to the dose of 147 mg/kg, does not affect normal blood and bone marrow cells at the therapeutically active dose, but strongly suppresses both primary tumor growth (confirmed in Nemeth-Kellner lymphoma and LLC1 lung cancer models of murine tumor) and spreading of metastases (LLC1).

We propose symmetrical cationic trimethine cyanine dyes with β-substituents in the polymethine chain based on modified benzothiazole and benzoxazole heterocycles as probes for the detection and visualization of live and fixed cells by fluorescence microscopy. The spectral-luminescent properties of trimethine cyanines have been characterized for free dyes and in the presence of nucleic acids (NA) and globular proteins. The studied cyanines are low to moderate fluorescent when free, but in the presence of NA, they show an increase in emission intensity up to 111 times; the most pronounced emission increase was observed for the dyes T-2 in the presence of dsDNA and T-1 with RNA. Spectral methods showed the binding of all dyes to nucleic acids, and different interaction mechanisms have been proposed. The ability to visualize cell components of the studied dyes has been evaluated using different human cell lines (MCF-7, A2780, HeLa, and Hs27). We have shown that all dyes are cell-permeant staining nucleus components, probably RNA-rich nucleoli with background fluorescence in the cytoplasm, except for the dye T-5. The dye T-5 selectively stains some structures in the cytoplasm of MCF-7 and A2780 cells associated with mitochondria or lysosomes. This effect has also been confirmed for the normal type of cell line-human foreskin fibroblasts (Hs27). The costaining of dye T-5 with MitoTracker CMXRos Red demonstrates specificity to mitochondria at a concentration of 0.1 μM. Colocalization analysis has shown signals overlapping of dye T-5 and MitoTracker CMXRos Red (Pearson's Coefficient value = 0.92 ± 0.04). The photostability study shows benzoxazole dyes to be up to ∼7 times more photostable than benzothiazole ones. Moreover, studied benzoxazoles are less cytotoxic at working concentrations than benzothiazoles (67% of cell viability for T-4, T-5 compared to 12% for T-1, and ∼30% for T-2, T-3 after 24 h). Therefore, the benzoxazole T-4 dye is proposed for nucleic acid detection in vitro and intracellular fluorescence imaging of live and fixed cells. In contrast, the benzoxazole dye T-5 is proposed as a good alternative to commercial dyes for mitochondria staining in the green-yellow region of the spectrum.

Two most common synthetic approaches (i.e. the esterification and 1,3-dipolar cycloaddition reactions) to a functionalization of the reactive three-dimensional molecular platforms, allowing to obtain the fluorescently labelled iron(II) clathrochelates and, therefore, to study their localization and accumulation in cancer cells, were compared. Because an esterification approach gave the target complexes in a very low yield, if any, such a functionalization of a known propargylamine iron(II) clathrochelate complex with terminal C C bond as a reactive macrobicyclic precursor by the copper-promoted 1,3-dipolar cycloaddition "click" reaction was also tested. This one-pot synthetic procedure allowed to obtain the cumarin-terminated iron(II) cage complex in a high yield; it was characterized using elemental analysis, ESI-TOF mass, and H-1 and C-13{H-1} NMR spectra.

Reactions of azide-alkilic cycloaddition are well known since 1893. At the same time, with the elaboration of click chemistry, the techniques of labelling biological objects, particularly by fluorescent dyes, were widely developed. The use of fluorescent labels provides the ability to visually monitor the process streamlines hardware load and reduces research time. Fluorescein is among the fluorophores mostly used for labelling of biomolecules due to its high quantum yields and good stability in biological media. However, despite of commercial availability of fluorescein derivatives functionalized for use in click reactions, methods for their synthesis are virtually absent in the literature. Therefore, we have developed a reliable and effective methodic for the synthesis of functionalized fluoresceines for the use in the click reactions. Synthesis of diacetyl N-(4-azidobutyl)-fluoresceine-5(6)-carboxamide was performed in six stages, starting form resorcinol and trimellitic acid anhydride. The diacetylated analogue was synthesized for the click modifications in the “soft” conditions, since N-(4-azidobutyl)-fluorescein-5(6)-carboxamide is poorly soluble in the classic organic solvents. Proposed synthetic protocol allows to increase the yield of the final and intermediate compounds and to optimized the procedure of their isolation and purification.

The heterodifunctionalized iron(II) clathrochelates, the molecules of which contain the terminal biorelevant carboxyl and reactive triple C C groups were obtained using the two-step synthetic procedures by a subsequent substitution of their dichloroclathrochelate precursor with para-carboxyphenylthiolate anion and 2-propargylamine. The complexes obtained were characterized using elemental analysis, HR-APPI and MALDI-TOF mass spectrometries, UV-Vis, H-1, C-13{H-1}, B-11 and F-19 NMR spectroscopies, and by the single crystal X-ray diffraction for an iron(II) monochloroclathrochelate with terminal propargylamine group. Its FeN6-coordination polyhedron possesses a distorted trigonal prismatic - trigonal-antiprismatic geometry with the average distortion angle phi of approximately 26.1 degrees. Fe-N distances in this monoribbed-functionalized molecule vary in a narrow range from 1.883(3) to 1.901(4) angstrom and the height h of the above polyhedron is equal to 2.30 angstrom. Cyclic voltammograms study of these complexes contain the single cathodic wave assigned to the metal-centered processes of the cathodic Fe2+/+ reduction and anodic Fe+/2+ re-oxidation, thus suggesting their quasi-reversible character. Chemical reactions (including a complete decomposition and a reductive hydrodehalogenation of the macrobicyclic molecules) of the propargylamine and propargylamide iron(II) clathrochelates was studied in various media and under the different experimental conditions using TLC, high-resolution APPI mass, NMR and UV-vis spectra, suggesting a complete slow destruction of the macrobicyclic frameworks of their molecules in aqueous solutions (including those modeling the physiological conditions).

Nowadays, the compounds with ethynyl group(s) are frequently used for their further modifications using the methods of modern so-called “click”-chemistry, based on the metalpromoted 1,3-dipolar cycloaddition reactions. We performed an attempt to obtain new monoribbed-difunctionalized clathrochelate iron(II) complexes with propargylamine- or propargylamide-terminated ribbed substituents as the prospective macrobicyclic precursors of their Sonogashira reactions. However, we observed an uncommon low chemical stability of these propargylamine and propargylamide cage complexes under basic conditions. In particular, the propargylamide substituent of the iron(II) complex 1 (Scheme) underwent a slow hydrolysis in the presence of triethylamine in its dichloromethane solution, thus giving the terminal carboxyl group, while, in the case, of the clathrochelate 2, its reductive elimination reaction occurred. The same result was observed after a stirring of the dichloromethane solution of this monopropargylamine iron(II) cage complex with NaHCO3 aqueous solution.

A new approach for performing Suzuki-Miyaura and Sonogashira reactions of iron(ii) dihalogenoclathrochelates, optimizing their reaction conditions (such as temperature, solvent and a palladium-containing catalyst) and the nature of other reagents (such as arylboron components) is elaborated. These palladium-catalyzed reactions are very sensitive to the nature of the macrobicyclic substrates. The reactivity of the leaving halogen atoms correlates with their ability to undergo an oxidative addition, decreasing in the order: I > Br > Cl, and iron(ii) diiodoclathrochelate underwent these C-C cross-couplings under their "classical" conditions. Phenylboronic, 4-carboxyphenylboronic and 6-ethoxy-2-naphthylboronic acids, and the diethyl ether of 4-(ethoxycarbonyl)boronic acid were tested as components of Suzuki-Miyaura reactions in DMF and in THF. The highest yields of the target products were obtained in DMF, while the highest activation was observed with sodium and potassium carbonates. The Suzuki-Miyaura reaction of a diiodoclathrochelate with 6-ethoxy-2-naphthylboronic acid gave the mono- and difunctionalized clathrochelates resulting from the tandem hydrodeiodination - C-C cross-coupling and double C-C cross-coupling reactions, respectively. Its Sonogashira reactions with trimethylsilylacetylene and acetylenecarboxylic acid in THF and in DMF were tested. This palladium-catalyzed reaction with a (CH3)3Si-containing active component gave the target products in a high total yield. The complexes obtained were characterized using elemental analysis, MALDI-TOF, UV-Vis, 1H and 13C{1H} NMR spectroscopy, and by single crystal XRD. Despite the non-equivalence of the ribbed α-dioximate fragments of their molecules, the encapsulated iron(ii) ion is situated almost in the centre of its FeN6-coordination polyhedron, the geometry of which is almost intermediate between a trigonal prism and a trigonal antiprism.