Maria Antonia Martin

The design and synthesis of a small library of 2-styrylquinoline derivatives containing a push-pull system, aimed at displacing their fluorescence emission towards the NIR region, is described. We describe here their synthesis, fluorescent characterization and pharmacological evaluation against different amyloid proteins. Their study showed that these compounds are capable to change their spectroscopic properties upon protein interaction, resulting in changes in the absorption and emission wavelengths, together with increased fluorescence intensity. They also showed sensitivity to pH and environment polarity, exhibiting red shifts in lower polarity environments with regard to aqueous media. Inner charge transfer is observed and employed for detecting the interaction of these compounds with protein aggregates. The study of the alterations in the fluorescence intensity allows to calculate the dissociation constant values for the protein-sensor interaction. These spectroscopic results were the basis for the use of these compounds to visualize β-amyloid plates with selectivity over phosphorylated tau in samples of cerebral tissue from deceased Alzheimer patients under fluorescence microscopy, using immunofluorescence techniques. Pharmacological assays showed that the compounds inhibit the aggregation of the Aβ_1–42 and AcPHF6 peptides, representing tau protein. They also showed neuroprotective activity following okadaic acid insult.

A group of functionalized fluorene derivatives that are structurally similar to the cellular prion protein ligand N,N′-(methylenedi-4,1-phenylene)bis [2-(1-pyrrolidinyl)acetamide] (GN8) have been synthesized. These compounds show remarkable native fluorescence due to the fluorene ring. The substituents introduced at positions 2 and 7 of the fluorene moiety are sufficiently flexible to accommodate the beta-conformational folding that develops in amyloidogenic proteins. Changes in the native fluorescence of these fluorene derivatives provide evidence of transformations in the amyloidogenic aggregation processes of insulin. The increase observed in the fluorescence intensity of the sensors in the presence of native insulin or amyloid aggregates suggest their potential use as fluorescence probes for detecting abnormal conformations; therefore, the compounds can be proposed for use as “turn-on” fluorescence sensors. Protein–sensor dissociation constants are in the 5–10 μM range and an intermolecular charge transfer process between the protein and the sensors can be successfully exploited for the sensitive detection of abnormal insulin conformations. The values obtained for the Stern–Volmer quenching constant for compound 4 as a consequence of the sensor–protein interaction are comparable to those obtained for the reference compound GN8. Fluorene derivatives showed good performance in scavenging reactive oxygen species (ROS), and they show antioxidant capacity according to the FRAP and DPPH assays.

Many active pharmaceutical ingredients show low oral bioavailability due to factors such as poor solubility and physical and chemical instability. The formation of inclusion complexes with cyclodextrins, as well as cyclodextrin-based polymers, nanosponges, and nanofibers, is a valuable tool to improve the oral bioavailability of many drugs. The microencapsulation process modifies key properties of the included drugs including volatility, dissolution rate, bioavailability, and bioactivity. In this context, we present relevant examples of the stabilization of labile drugs through the encapsulation in cyclodextrins. The formation of inclusion complexes with drugs belonging to class IV in the biopharmaceutical classification system as an effective solution to increase their bioavailability is also discussed. The stabilization and improvement in nutraceuticals used as food supplements, which often have low intestinal absorption due to their poor solubility, is also considered. Cyclodextrin-based nanofibers, which are polymer-free and can be generated using environmentally friendly technologies, lead to dramatic bioavailability enhancements. The synthesis of chemically modified cyclodextrins, polymers, and nanosponges based on cyclodextrins is discussed. Analytical techniques that allow the characterization and verification of the formation of true inclusion complexes are also considered, taking into account the differences in the procedures for the formation of inclusion complexes in solution and in the solid state.

The environmental presence of anions of natural origin or anthropogenic origin is gradually increasing. As a tool to tackle this problem, carbazole derivatives are an attractive gateway to the development of luminescent chemosensors. Considering the different mechanisms proposed for anion recognition, the fluorescence properties and anion-binding response of several newly synthesised carbazole derivatives were studied. Potential anion sensors were designed so that they combined the native fluorescence of carbazole with the presence of hydrogen bonding donor groups in critical positions for anion recognition. These compounds were synthesised by a feasible and non-expensive procedure using palladium-promoted cyclodehydrogenation of suitable diarylamine under microwave irradiation. In comparison to the other carbazole derivatives studied, 1-hydroxycarbazole proved to be useful as a fluorescent sensor for anions, as it was able to sensitively recognise fluoride and chloride anions by establishing hydrogen bond interactions through the hydrogen atoms on the pyrrolic nitrogen and the hydroxy group. Solvent effects and excited-state proton transfer (ESPT) of the carbazole derivatives are described to discard the role of the anions as Brönsted bases on the observed fluorescence behaviour of the sensors. The anion–sensor interaction was confirmed by ¹H-NMR. Molecular modelling was employed to propose a mode of recognition of the sensor in terms of complex stability and interatomic distances. 1-hydroxycarbazole was employed for the quantitation of fluoride and chloride anions in commercially available medicinal spring water and mouthwash samples.

Supramolecular chemistry involves non-covalent interactions and specific molecular recognition of molecules/analytes by host molecules or supramolecules. These events are present in synthesis, catalysis, chiral separations, design of sensors, cell signaling processes and drug transport by carriers. The typical behavior of supramolecules is derived from their ability to build well-structured self-assembled and self-organized entities. Cavitands are a particular group of supramolecules possessing a cavity able to include a variety of compounds thanks to host-guest non-covalent interactions developed among cavitands and analytes. Some typical cavitands are crown ethers, calixarenes, cucurbiturils, porphyrins and cyclodextrins. The two latter families are natural product cavitands that are generally considered models for molecular recognition of cations and organic and inorganic guest molecules, being attractive host molecules from the sustainability point of view. The natural cyclodextrins (𝛼-, 𝛽- and 𝛾-CD) are obtained with reasonable cost by enzymatic treatment of starch under adequate temperature conditions. They are profusely used in pharmaceutical, food and cosmetic industries due to their very low toxicity and side effects. This review is focused on the relevance and applications of cyclodextrins in pharmaceutical technology for their ability to increase solubility and stabilize drug molecules, thereby enhancing their bioavailability. The association of cyclodextrins with diverse nanostructured materials, i.e. carbon nanotubes, magnetic nanoparticles, silica and molecularly imprinted polymers, allows to synergize the properties of cyclodextrins and these nanostructured materials to reach highly specific molecular recognition of analytes. The exploitation of these benefits for analytical sample pre-treatment and chiral chromatographic separations are described. The use of cyclodextrins as mobile phases additives in HPLC provides interesting results for green and sustainable chromatographic separations. Polymers incorporating cyclodextrins show exceptional adsorption properties for retaining toxic compounds and persistent organic pollutants from soils and water samples, allowing satisfactory recoveries of these environmental samples according to the Stockholm convection principles.

The use of cyclodextrins as drug nano-carrier systems for drug delivery is gaining importance in the pharmaceutical industry due to the interesting pharmacokinetic properties of the resulting inclusion complexes. In the present work, complexes of the anti-cancer alkaloids camptothecin and luotonin A have been prepared with β-cyclodextrin and hydroxypropyl-β-cyclodextrin. These cyclodextrin complexes were characterized by nuclear magnetic resonance spectroscopy (NMR). The variations in the ¹H-NMR and ¹³C-NMR chemical shifts allowed to establish the inclusion modes of the compounds into the cyclodextrin cavities, which were supported by docking and molecular dynamics studies. The efficiency of the complexation was quantified by UV-Vis spectrophotometry and spectrofluorimetry, which showed that the protonation equilibria of camptothecin and luotonin A were drastically hampered upon formation of the inclusion complexes. The stabilization of camptothecin towards hydrolysis inside the cyclodextrin cavity was verified by the quantitation of the active lactone form by reverse phase liquid chromatography fluorimetric detection, both in basic conditions and in the presence of serum albumin. The antitumor activity of luotonin A and camptothecin complexes were studied in several cancer cell lines (breast, lung, hepatic carcinoma, ovarian carcinoma and human neuroblastoma) and an enhanced activity was found compared to the free alkaloids, particularly in the case of hydroxypropyl-β-cyclodextrin derivatives. This result shows that the cyclodextrin inclusion strategy has much potential towards reaching the goal of employing luotonin A or its analogues as stable analogues of camptothecin.

Oxidative stress is crucial to the outbreak and advancement of neurodegenerative diseases and is a common factor to many of them. We describe the synthesis of a library of derivatives of the 4-arylmethylen-2-pyrrolin-5-one framework by sequential application of a three-component reaction of primary amines, β-dicarbonyl compounds, and α-haloketones and a Knoevenagel condensation. These compounds can be viewed as cyclic amides of caffeic and ferulic acids, and are also structurally related to the bisavenanthramide family of natural antioxidants. Most members of the library showed low cytotoxicity and good activity as inductors of Nrf2, a transcription factor that acts as the master regulator of the antioxidant response associated with activation of the antioxidant response element (ARE). Nrf2-dependent protein expression was also proved by the significant increase in the levels of the HMOX1 and NQO1 proteins. Some compounds exerted neuroprotective properties in oxidative stress situations, such as rotenone/oligomycin-induced toxicity, and also against protein hyperphosphorylation induced by the phosphatase inhibitor okadaic acid. Compound 3i, which can be considered a good candidate for further hit-to-lead development against neurodegenerative diseases due to its well-balanced multitarget profile, was further characterized by proving its ability to reduce phosphorylated Tau levels.