Structure-based design of multitargeting ChEs-MAO B inhibitors based on phenyl ring bioisosteres: AChE/BChE selectivity switch and drug-like characterization.

A structure-based drug design approach was focused on incorporating phenyl ring heterocyclic bioisosteres into coumarin derivative 1, previously reported as potent dual AChE-MAO B inhibitor, with the aim of improving drug-like features. Structure-activity relationships highlighted that bioisosteric rings were tolerated by hMAO B enzymatic cleft more than hAChE. Interestingly, linker homologation at the basic nitrogen enabled selectivity to switch from hAChE to hBChE. In the present work, we identified thiophene-based isosteres 7 and 15 as dual AChE-MAO B (IC50 = 261 and 15 nM, respectively) and BChE-MAO B (IC50 = 375 and 20 nM, respectively) inhibitors, respectively. Both 7 and 15 were moderately water-soluble and membrane-permeant agents by passive diffusion (PAMPA-HDM). Moreover, they were able to counteract oxidative damage induced by both H2O2 and 6-OHDA in SH-SY5Y cells and predicted to penetrate into CNS in a cell-based model mimicking blood-brain barrier. Molecular dynamics (MD) simulations shed light on key differences in AChE and BChE recognition processes promoted by the basic chain homologation from 7 to 15.

Discovery and Structure-Activity Relationships of Novel ssDAF-12 Receptor Modulators.

The nuclear receptor ssDAF-12 has been recognized as the key molecular player regulating the life cycle of the nematode parasite Strongyloides stercoralis. ssDAF-12 ligands permit the receptor to function as an on/off switch modulating infection, making it vulnerable to therapeutic intervention. In this study, we report the design and synthesis of a set of novel dafachronic acid derivatives, which were used to outline the first structure-activity relationship targeting the ssDAF-12 receptor and to unveil hidden properties shared by the molecular shape of steroidal ligands that are relevant to the receptor binding and modulation. Moreover, biological results led to the discovery of sulfonamide 3 as a submicromolar ssDAF-12 agonist endowed with a high receptor selectivity, no toxicity, and improved properties, as well as to the identification of unprecedented ssDAF-12 antagonists that can be exploited in the search for novel chemical tools and alternative therapeutic approaches for treating parasitism such as Strongyloidiasis.

3-O-Methyltolcapone and Its Lipophilic Analogues Are Potent Inhibitors of Transthyretin Amyloidogenesis with High Permeability and Low Toxicity.

Transthyretin (TTR) is an amyloidogenic homotetramer involved in the transport of thyroxine in blood and cerebrospinal fluid. To date, more than 130 TTR point mutations are known to destabilise the TTR tetramer, leading to its extracellular pathological aggregation accumulating in several organs, such as heart, peripheral and autonomic nerves, and leptomeninges. Tolcapone is an FDA-approved drug for Parkinson's disease that has been repurposed as a TTR stabiliser. We characterised 3-O-methyltolcapone and two newly synthesized lipophilic analogues, which are expected to be protected from the metabolic glucuronidation that is responsible for the lability of tolcapone in the organism. Immunoblotting assays indicated the high degree of TTR stabilisation, coupled with binding selectivity towards TTR in diluted plasma of 3-O-methyltolcapone and its lipophilic analogues. Furthermore, in vitro toxicity data showed their several-fold improved neuronal and hepatic safety compared to tolcapone. Calorimetric and structural data showed that both T4 binding sites of TTR are occupied by 3-O-methyltolcapone and its lipophilic analogs, consistent with an effective TTR tetramer stabilisation. Moreover, in vitro permeability studies showed that the three compounds can effectively cross the blood-brain barrier, which is a prerequisite for the inhibition of TTR amyloidogenesis in the cerebrospinal fluid. Our data demonstrate the relevance of 3-O-methyltolcapone and its lipophilic analogs as potent inhibitors of TTR amyloidogenesis.

Probing Fluorinated Motifs onto Dual AChE-MAO B Inhibitors: Rational Design, Synthesis, Biological Evaluation, and Early-ADME Studies.

Bioisosteric H/F or CH2OH/CF2H replacement was introduced in coumarin derivatives previously characterized as dual AChE-MAO B inhibitors to probe the effects on both inhibitory potency and drug-likeness. Along with in vitro screening, we investigated early-ADME parameters related to solubility and lipophilicity (Sol7.4, CHI7.4, log D7.4), oral bioavailability and central nervous system (CNS) penetration (PAMPA-HDM and PAMPA-blood-brain barrier (BBB) assays, Caco-2 bidirectional transport study), and metabolic liability (half-lives and clearance in microsomes, inhibition of CYP3A4). Both specific and nonspecific tissue toxicities were determined in SH-SY5Y and HepG2 lines, respectively. Compound 15 bearing a -CF2H motif emerged as a water-soluble, orally bioavailable CNS-permeant potent inhibitor of both human AChE (IC50 = 550 nM) and MAO B (IC50 = 8.2 nM, B/A selectivity > 1200). Moreover, 15 behaved as a safe and metabolically stable neuroprotective agent, devoid of cytochrome liability.

Parallel and Multivalued Logic by the Two-Dimensional Photon-Echo Response of a Rhodamine−DNA Complex.

Implementing parallel and multivalued logic operations at the molecular scale has the potential to improve the miniaturization and efficiency of a new generation of nanoscale computing devices. Two-dimensional photon-echo spectroscopy is capable of resolving dynamical pathways on electronic and vibrational molecular states. We experimentally demonstrate the implementation of molecular decision trees, logic operations where all possible values of inputs are processed in parallel and the outputs are read simultaneously, by probing the laser-induced dynamics of populations and coherences in a rhodamine dye mounted on a short DNA duplex. The inputs are provided by the bilinear interactions between the molecule and the laser pulses, and the output values are read from the two-dimensional molecular response at specific frequencies. Our results highlights how ultrafast dynamics between multiple molecular states induced by light−matter interactions can be used as an advantage for performing complex logic operations in parallel, operations that are faster than electrical switching.

Time-Resolved Fluorescence Anisotropy of Bicyclo[1.1.1]pentane/Tolane-Based Molecular Rods Included in Tris(o-phenylenedioxy)cyclotriphosphazene (TPP).

We examine the fluorescence anisotropy of rod-shaped guests held inside the channels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) host nanocrystals, characterized by powder X-ray diffraction and solid state NMR spectroscopy. We address two issues: (i) are light polarization measurements on an aqueous colloidal solution of TPP nanocrystals meaningful, or is depolarization by scattering excessive? (ii) Can measurements of the rotational mobility of the included guests be performed at low enough loading levels to suppress depolarization by intercrystallite energy transfer? We find that meaningful measurements are possible and demonstrate that the long axis of molecular rods included in TPP channels performs negligible vibrational motion.

Light and pH tunable luminescence in a photochromic bisdiarylethene.

In this work the luminescence of a bisdiarylethene, containing a benzobis(imidazole) core substituted with two aniline moieties, has been investigated. In previous research, it was found that both acidification and irradiation reversibly triggered colour changes of this compound, thus generating a multi-responsive acidichromic and photochromic system. Intense fluorescence emission, which was detected in several organic solvents, can be an additional light driven signal. In a dioxane/water (1 : 1, v/v) mixture, intensity and spectral position of luminescence have been found to drastically depend on the pH/H0 values of the solutions (pH 5/H0-2 range) due to subsequent protonations (four steps) as the acidity of the solution changes. Alternated irradiations with UV and visible light lead to a decrease and increase, respectively, of the fluorescence intensity, due to the photochromic reaction producing a non-fluorescent compound. Quantum yields and lifetimes of fluorescence were determined as a function of the acidity. The results indicate that protonation shifts the emission to the red and decreases its intensity. The possibility of tuning the colour and intensity of luminescence by both acidification and irradiation generates a multi-switchable "fluorochromic" material.

Tetra- and tri-thienyl ethenes: new fluorescent photochromic compounds.

In this work the photochemistry and photophysics of two new ethenic compounds, a tetra-thienylethene (tetrakis) and a tri-thienylethene (triakis), have been investigated by steady state and time-resolved UV-vis absorption and luminescence spectroscopies. The quantum yields of the UV-photoinduced ring-closure reaction (Φ(O→C)) and of the visible-stimulated cycloreversion reaction (Φ(C→O)) were determined as a function of the temperature in 3-methylpentane. The trends of Φ(O→C) and Φ(C→O) with temperature suggest that a barrier exists to the ring opening reaction which hampers the cycloreversion in a rigid matrix at 80 K. For the closure reaction, a negative effect of the temperature on Φ(O→C) reflects an increased concentration of the more easily isomerizable antiparallel conformer with decreasing the temperature. Quantum yields and lifetimes of fluorescence, observed for tetrakis in both the colourless and coloured forms and for triakis only for the coloured form, were determined. The solvent and temperature effects on fluorescence were investigated. Nanosecond time-resolved experiments showed the formation of a triplet transient from tetrakis which could be a precursor of the main reaction photoproduct. For triakis no transient was detected.

New thermally irreversible and fluorescent photochromic diarylethenes.

A photokinetic investigation is here carried out on four newly synthesized diarylethenes with the aim to test their performance as photoreversible chromogenic and light emitting materials. The pentatomic ring, which fixes these diarylethenes in the cis conformation, contains a Si atom or a PO group. The 1,2 positions at the ethenic bond are symmetrically substituted with thienyl or benzothienyl groups. The results are compared with those for the structurally related and widely studied 1,2-bis(2-methyl-benzo[b]thiophen-3-yl)perfluorocyclopentene (BTF6), investigated here under the same experimental conditions. Spectra of the colorless and colored forms and photoreaction quantum yields were determined; temperature, excitation wavelength and viscosity effects were explored. Compounds containing benzothienyl substituents were found to be good bistable photochromes, with high photochemical yields of both the cyclization and cycloreversion reactions, and to display appreciable fluorescence emission from the colored forms, which is a rare and desirable property for photochromes. In contrast, the molecules not bearing the benzene condensed rings were found unsuitable as photochromes because of side degradation processes occurring in competition with cyclization.