Circular dichroism in drug discovery and development: an abridged review

Chirality plays a fundamental role in determining the pharmacodynamic and pharmacokinetic properties of drugs, and contributes significantly to our understanding of the mechanisms that lie behind biorecognition phenomena. Circular dichroism spectroscopy is the technique of choice for determining the stereochemistry of chiral drugs and proteins, and for monitoring and characterizing molecular recognition phenomena in solution. The role of chirality in our understanding of recognition phenomena at the molecular level is discussed here via several selected systems of interest in the drug discovery and development area. The examples were selected in order to underline the utility of circular dichroism in emerging studies of protein–protein interactions in biological context. In particular, the following aspects are discussed here: the relationship between stereochemistry and pharmacological activity—stereochemical characterization of new leads and drugs; stereoselective binding of leads and drugs to target proteins—the binding of drugs to serum albumins; conformational transitions of peptides and proteins of physiological relevance, and the stereochemical characterization of therapeutic peptides.     

Solvent- and temperature-dependent functionalisation of enantioenriched aziridines

A highly stereo‐ and regioselective functionalisation of chiral non‐racemic aziridines is reported. By starting from a parent enantioenriched aziridine and finely tuning the reaction conditions, it is possible to address the regio‐ and stereoselectivity of the lithiation/electrophile trapping sequence, thereby allowing the preparation of highly enantioenriched functionalised aziridines. From chiral N‐alkyl trans‐2,3‐diphenylaziridines (S,S)‐ 1 a , b , two differently configured chiral aziridinyllithiums could be generated (trans‐ 1 a , b‐Li in toluene and cis‐ 1 a , b‐Li in THF), thus disclosing a solvent‐dependent reactivity that is useful for the synthesis of chiral tri‐substituted aziridines with different stereochemistry. In contrast, chiral aziridine (S,S)‐ 1 c showed a temperature‐dependent reactivity to give chiral ortho‐lithiated aziridine 1 c‐ ortho ‐Li at ?78 °C and α‐lithiated aziridine 1 c‐α‐Li at 0 °C. Both lithiated intermediates react with electrophiles to give enantioenriched ortho‐ and α‐functionalised aziridines. The reaction of all the lithiated aziridines with carbonyl compounds furnished useful chiral hydroxyalkylated derivatives, the stereochemistry of which was ascertained by X‐ray and NMR spectroscopic analysis. The usefulness of chiral non‐racemic functionalised aziridines has been demonstrated by reductive ring‐opening reactions furnishing chiral amines that bear quaternary stereogenic centres and chiral 1,2‐, 1,3‐ and 1,5‐aminoalcohols. It is remarkable that the solvent‐dependent reactivity observed with (S,S)‐ 1 a , b permits the preparation of both the enantiomers of amines ( 11 and ent‐ 11 ) and 1,2‐aminoalcohols ( 13 and ent‐ 13 ) starting from the same parent aziridine. Interestingly, for the first time, a configurationally stable chiral α‐lithiated aziridine ( 1 c‐α‐Li ) has been generated at 0 °C. In addition, ortho‐hydroxyalkylated aziridines have been easily converted into chiral aminoalkyl phthalans, which are useful building blocks in medicinal chemistry.     

Investigation of Solvatomorphism and Its Photophysical Implications for Archetypal Trinuclear Au3(1-Methylimidazolate)3

A new solvatomorph of [Au₃(1-Methylimidazolate)₃] (Au₃(MeIm)₃)—the simplest congener of imidazolate-based Au(I) cyclic trinuclear complexes (CTCs)—has been identified and structurally characterized. Single-crystal X-ray diffraction revealed a dichloromethane solvate exhibiting remarkably short intermolecular Au⋯Au distances (3.2190(7) Å). This goes along with a dimer formation in the solid state, which is not observed in a previously reported solvent-free crystal structure. Hirshfeld analysis, in combination with density functional theory (DFT) calculations, indicates that the dimerization is generally driven by attractive aurophilic interactions, which are commonly associated with the luminescence properties of CTCs. Since Au₃(MeIm)₃ has previously been reported to be emissive in the solid-state, we conducted a thorough photophysical study combined with phase analysis by means of powder X-ray diffraction (PXRD), to correctly attribute the photophysically active phase of the bulk material. Interestingly, all investigated powder samples accessed via different preparation methods can be assigned to the pristine solvent-free crystal structure, showing no aurophilic interactions. Finally, the observed strong thermochromism of the solid-state material was investigated by means of variable-temperature PXRD, ruling out a significant phase transition being responsible for the drastic change of the emission properties (hypsochromic shift from 710 nm to 510 nm) when lowering the temperature down to 77 K.     

X-Ray Crystal Structure of Phyllostin,a Metabolite Produced by <Emphasis Type="Italic">Phyllosticta cirsii</Emphasis>, a Potential Mycoherbicide of <Emphasis Type="Italic">Cirsium arvense</Emphasis>

Abstract  

The X-ray crystal structure of phyllostin (8-hydroxy-3-methyl-2-oxo-2,3,4a,5,8,8a-hexahydro-benzo[1,4]dioxine-6-carboxylic acid methyl ester) is reported. Phyllostin was recently and for the first time isolated, together with phytotoxin phyllostoxin and the phyllostictines A–D, from the culture filtrates of Phyllosticta cirsii, a fungal pathogen isolated from diseased Cirsium arvense leaves and evaluated as biocontrol agent of this noxious perennial weed. Phyllostin crystallizes in the monoclinic space group P2₁ with unit cell parameters: a = 8.371(2), b = 7.026(1), c = 9.918(1) ?, β = 92.013(8)°, Z = 2. The final refinement converged to R1 = 0.0530 for 1026 observed reflections having I > 2σ(I). In the molecule two trans joined six-membered rings are present. The cyclohexene ring adopts a half-chair conformation. The 2-oxo-1,4-dioxan ring adopts a distorted half-chair conformation. The relative stereochemistry of the four chiral centers turns out to be 3R,4aS,8R,8aS. In the crystal packing molecules form infinite chains through O–H···O intermolecular hydrogen bonds. Chains run along the crystallographic a axis forming layers of molecules stacking in the [0 1 0] direction.     

Tuning hydrophobicity of platinum by small changes in surface morphology

Stepped platinum surfaces can become hydrophobic when they are hydrogenated. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on Pt(553).     

Generation and near-field imaging of Airy surface plasmons

We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves, plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation.     

Three-dimensional in vivo scanning microscopy with inertia-free focus control

The acquisition of high-resolution images in three dimensions is of utmost importance for the morphological and functional investigation of biological tissues. Here, we present a laser scanning two-photon microscope with remote and motionless control of the focus position. The movement of the excitation spot along the propagation direction is achieved by shaping the laser wavefront with a spatial light modulator. Depending on the optical properties of the objective in use, this approach allows z movements in a range of tens to hundreds of micrometers with small changes of the point spread function. We applied this technique for the three-dimensional (3D) imaging of fluorescent cells in the mouse neocortex in vivo. The presented system bypasses the limitations of microscopes based on moving objectives, enabling high-resolution inertia-free 3D imaging.     

Screening of magnetic fields by charged Bose condensate

The space-space component of the photon polarization operator is calculated in zero frequency limit for a medium with Bose-Einstein condensate (BEC) of electrically charged particles. It is found that the polarization operator tends to a finite value at vanishing photon 3-momentum, as it happens in superconducting media. It means that magnetic fields are exponentially screened in such a medium analogously to the Debye screening of electric charges. At non-zero temperature the screened magnetic field oscillates and contains a contribution which drops only as a power of distance. This phenomenon is unknown for superconductors, even in BEC phase and can be potentially observable.     

Effective location models for sorting recyclables in public management

The recycling of urban solid wastes is a critical point for the “closing supply chains” of many products, mainly when their value cannot be completely recovered after use. In addition to environmental aspects, the process of recycling involves technical, economic, social and political challenges for public management. For most of the urban solid waste, the management of the end-of-life depends on selective collection to start the recycling process. For this reason, an efficient selective collection has become a mainstream tool in the Brazilian National Solid Waste Policy. In this paper, we study effective models that might support the location planning of sorting centers in a medium-sized Brazilian city that has been discussing waste management policies over the past few years. The main goal of this work is to provide an optimal location planning design for recycling urban solid wastes that fall within the financial budget agreed between the municipal government and the National Bank for Economic and Social Development. Moreover, facility planning involves deciding on the best sites for locating sorting centers along the four-year period as well as finding ways to meet the demand for collecting recyclable materials, given that economic factors, consumer behavior and environmental awareness are inherently uncertain future outcomes. To deal with these issues, we propose a deterministic version of the classical capacity facility location problem, and both a two-stage recourse formulation and risk-averse models to reduce the variability of the second-stage costs. Numerical results suggest that it is possible to improve the current selective collection, as well as hedge against data uncertainty by using stochastic and risk-averse optimization models.