An Insight into Symmetrical Cyanine Dyes as Promising Selective Antiproliferative Agents in Caco-2 Colorectal Cancer Cells.

Cancer remains one of the diseases with the highest worldwide incidence. Several cytotoxic approaches have been used over the years to overcome this public health threat, such as chemotherapy, radiotherapy, and photodynamic therapy (PDT). Cyanine dyes are a class of compounds that have been extensively studied as PDT sensitisers; nevertheless, their antiproliferative potential in the absence of a light source has been scarcely explored. Herein, the synthesis of eighteen symmetric mono-, tri-, and heptamethine cyanine dyes and their evaluation as potential anticancer agents is described. The influences of the heterocyclic nature, counterion, and methine chain length on the antiproliferative effects and selectivities were analysed, and relevant structure-activity relationship data were gathered. The impact of light on the cytotoxic activity of the most promising dye was also assessed and discussed. Most of the monomethine and trimethine cyanine dyes under study demonstrated a high antiproliferative effect on human tumour cell lines of colorectal (Caco-2), breast (MCF-7), and prostate (PC-3) cancer at the initial screening (10 µM). However, concentration-viability curves showed higher potency and selectivity for the Caco-2 cell line. A monomethine cyanine dye derived from benzoxazole was the most promising compound (IC50 for Caco-2 = 0.67 µM and a selectivity index of 20.9 for Caco-2 versus normal human dermal fibroblasts (NHDF)) and led to Caco-2 cell cycle arrest at the G0/G1 phase. Complementary in silico studies predicted good intestinal absorption and oral bioavailability for this cyanine dye.

Squaraine Dyes Derived from Indolenine and Benzo[e]indole as Potential Fluorescent Probes for HSA Detection and Antifungal Agents.

Four squaraine dyes derived from 2,3,3-trimethylindolenine and 1,1,2-trimethyl-1H-benzo[e]indole with different combinations of barbituric groups attach to the central ring, having ester groups and alkyl chains in the nitrogen atoms of heterocyclic rings were synthesized. These dyes were fully characterized, and their photophysical behavior was studied in ethanol and phosphate-buffered solution. Absorption and emission bands between 631 and 712 nm were detected, with the formation of aggregates in aqueous media, which is typical of this class of dyes. Tests carried out with 1,3-diphenylisobenzofuran allowed us to verify the ability of the dyes to produce singlet oxygen. The interaction of synthesized dyes with human serum albumin (HSA) was also evaluated, being demonstrated a linear correlation between fluorescence intensity and protein concentration. The antifungal potential of the dyes against the yeast Saccharomyces cerevisiae was evaluated using a broth microdilution assay. In order to test the photosensitizing capacity of the synthesized dyes, tests were carried out in the dark and with irradiation, using a custom-built light-emitting diode that emits close to the absorption wavelength of the studied dyes. The results showed that the interaction of dyes with HSA and the antifungal activity depends on the different structural modifications of the dyes.

Bis-thiobarbiturates as Promising Xanthine Oxidase Inhibitors: Synthesis and Biological Evaluation.

Xanthine oxidase (XO) is the enzyme responsible for the conversion of endogenous purines into uric acid. Therefore, this enzyme has been associated with pathological conditions caused by hyperuricemia, such as the disease commonly known as gout. Barbiturates and their congeners thiobarbiturates represent a class of heterocyclic drugs capable of influencing neurotransmission. However, in recent years a very large group of potential pharmaceutical and medicinal applications have been related to their structure. This great diversity of biological activities is directly linked to the enormous opportunities found for chemical change off the back of these findings. With this in mind, sixteen bis-thiobarbiturates were synthesized in moderate to excellent reactional yields, and their antioxidant, anti-proliferative, and XO inhibitory activity were evaluated. In general, all bis-thiobarbiturates present a good antioxidant performance and an excellent ability to inhibit XO at a concentration of 30 µM, eight of them are superior to those observed with the reference drug allopurinol (Allo), nevertheless they were not as effective as febuxostat. The most powerful bis-thiobarbiturate within this set showed in vitro IC50 of 1.79 µM, which was about ten-fold better than Allo inhibition, together with suitable low cytotoxicity. In silico molecular properties such as drug-likeness, pharmacokinetics, and toxicity of this promising barbiturate were also analyzed and herein discussed.

Synthesis and process optimization of symmetric and unsymmetric barbiturates C5-coupled with 2,1-benzisoxazoles.

Benzisoxazoles represent an important pharmacophore in medicinal chemistry. Recently, an unexpected formation of symmetric 3-substituted 2,1-benzisoxazoles through reduction of 5-(2-nitrobenzylidene)barbiturates has been described. This reductive intramolecular heterocyclization probably involves a nitroso intermediary. To improve the previous reaction conditions, the nature of the reducing agent and additives, reaction time and solvents were evaluated. By applying the optimized conditions, several symmetric and unsymmetric barbiturates C5-coupled with 2,1-benzisoxazoles were prepared with an yield of 52-87%. From this set, seven compounds were novel and the unsymmetric nature of the (thio)barbituric acid moiety was explored. For that, the total synthesis, starting from the respective urea or thiourea, was successfully performed, and 11 thiobarbiturates, benzylidene barbiturate and thiobarbiturate precursors are described.

NMR screening of new carbocyanine dyes as ligands for affinity chromatography.

Four new carbocyanines containing symmetric and asymmetric heterocyclic moieties and N-carboxyalkyl groups have been synthesized and characterized. The binding mechanism established between these cyanines and several proteins was evaluated using saturation transfer difference (STD) NMR. The results obtained for the different dyes revealed a specific interaction to the standard proteins lysozyme, α-chymotrypsin, ribonuclease (RNase), bovine serum albumin (BSA), and gamma globulin. For instance, the two un-substituted symmetrical dyes (cyanines 1 and 3) interacted preferentially through its benzopyrrole and dibenzopyrrole units with lysozyme, α-chymotrypsin, and RNase, whereas the symmetric disulfocyanine dye (cyanine 2) bound BSA and gamma globulin through its carboxyalkyl chains. On the other hand, the asymmetric dye (cyanine 4) interacts with lysozyme and α-chymotrypsin through benzothiazole moiety and with RNase through dibenzopyrrole unit. Thus, STD-NMR technique was successfully used to screen cyanine-protein interactions and determine potential binding sites of the cyanines for posterior use as ligands in affinity chromatography.

Study of specific interaction between nucleotides and dye support by nuclear magnetic resonance.

The binding between four matrices (beaded cellulose, cellulose acetate, cellulose triacetate and Sepharose CL-6B) and beaded cellulose derivatized with a thiacarbocyanine dye with 5'-mononucleotides is investigated by Saturation Transfer Difference Nuclear Magnetic Resonance (STD-NMR) technique. This procedure intends to identify unspecific interactions between 5'-mononucleotides and matrices commonly used in affinity chromatography systems and also clarify the contribution of a thiacarbocyanine dye immobilized onto cellulose beads in a biorecognition process. The differences between non-derivatized and derivatized beaded cellulose evidence the contribution of thiacarbocyanine dye in the observed interaction. STD-NMR experiments show that Sepharose CL- 6B interact less with the 5'-mononucleotides comparatively with beaded cellulose. Indeed, beaded cellulose shows nonspecific interactions with almost all 5'-mononucleotides that compromises the specificity of the interaction between the thiacarbocyanine dye immobilized with the 5'-mononucleotides. The cellulose matrices where the hydroxyl groups are replaced by acetate and triacetate groups do not exhibit binding response to the 5'- mononucleotides, whereas the thiacarbocyanine dye contribution is evidenced by the reinforcement of the interactions with the sugar moiety of 5'-GMP and 5'-UMP and with base of 5'-AMP, 5'-CMP and 5'-TMP. This screening of the nucleotide atoms involved in the binding to the supports can be very useful in chromatography evaluations in which dye-affinity chromatography supports may be used, such as purification of nucleic acids.

Rhodamine B as ligand for affinity chromatography: chromatographic studies on derivatized beaded cellulose.

Rhodamine B (RB) post-grafted onto beaded cellulose by a curing method is used as a biomimetic ligand in dye affinity chromatography. The grafted materials obtained are qualitatively characterized by scanning electron microscope and fourier transformed infrared spectroscopy. An amount of 76.79 mmol RB/g dyed cellulose is determined by elemental analysis. The RB affinity interaction with the trypsin, alpha-chymotrypsin, and BSA (bovine serum albumin) is analyzed using different mobile phase composition. The results show a selective separation of a mixture of BSA and trypsin into two single peaks by step elution with 1.75 M, 0.5 M, and 0 M ammonium sulphate in the eluent buffer. A good reproducibility of the retention time is obtained for these proteins in the mixture with typical values of 8.0 +/- 0.2 min for BSA and 20.0 +/- 0.2 min for trypsin, showing a possible application in the purification of samples with different composition.