Influence of heterochirality on the structure, dynamics, biological properties of cyclic(PFPF) tetrapeptides obtained by solvent-free ball mill mechanosynthesis.

Cyclic tetrapeptides c(Pro-Phe-Pro-Phe) obtained by the mechanosynthetic method using a ball mill were isolated in a pure stereochemical form as a homochiral system (all L-amino acids, sample A) and as a heterochiral system with D configuration at one of the stereogenic centers of Phe (sample B). The structure and stereochemistry of both samples were determined by X-ray diffraction studies of single crystals. In DMSO and acetonitrile, sample A exists as an equimolar mixture of two conformers, while only one is monitored for sample B. The conformational space and energetic preferences for possible conformers were calculated using DFT methods. The distinctly different conformational flexibility of the two samples was experimentally proven by Variable Temperature (VT) and 2D EXSY NMR measurements. Both samples were docked to histone deacetylase HDAC8. Cytotoxic studies proved that none of the tested cyclic peptide is toxic.

Molecular Dynamics of Steroidal Rotors Probed by Theoretical, Spectroscopic and Dielectric Methods.

Our study focuses on molecular rotors with fast-moving rotators and their potential applications in the development of new amphidynamic crystals. Steroidal molecular rotors with a dipolar fluorine-substituted phenyl group as the rotator were synthesized and characterized. Three different rotors were investigated with varying numbers of fluorine atoms. A comprehensive analysis was performed using vibrational spectroscopy (Raman, FT-IR), electronic circular dichroism (ECD), and dielectric response to understand the behavior of the investigated model rotors. The results were supported by theoretical calculations using Density Functional Theory (DFT) methods. The angle-dependent polarized Raman spectra confirmed the crystallinity of the samples. Nearly frequency and temperature-independent permittivity suggest low-frequency librational motion of stators. An in-depth analysis of ECD spectra revealed high conformational flexibility in solution, resulting in low ECD effects, while in the solid-state with restricted rotation, significant ECD effects were observed. These findings shed light on the conformational behavior and potential applications of the studied steroidal molecular rotors.

Differentiation of solvatomorphs of active pharmaceutical ingredients (API) by solid-state vibrational circular dichroism (VCD).

Here, we present the new application of solid-state Vibrational Circular Dichroism (VCD) spectroscopy to differentiate several dutasteride (DS) solvatomorphs - the model active pharmaceutical ingredient (API). Several crystalline DS hydrochloride hydrates solvated with methanol, ethanol, acetonitrile, acetone, and acetic acid were prepared. In contrast to almost identical IR spectra, the VCD ones were very sensitive to changes in the sample composition. We marked significant differences in the shape of VCD spectra of studied DS solvatomorphs, DS hydrates, and DS polymorphic forms. Our findings, supported by DFT calculations, show that VCD spectroscopy has the pronounced ability to distinguish their crystal arrangements. We believe that this contribution will extend the use of VCD in the pharmaceutical industry for developing and designing new chiral drug products for the identification, description, and in-depth probing of several pharmaceutical solvatomorphs in the future.

Strong Chiroptical Effects in the Absorption and Emission of Macrocycles Based on the 2,5-Diaminoterephthalate Minimal Fluorophore.

Chiral fluorescent macrocycles consisting of two to four units of dimethyl 2,5-diaminoterephthalate can be readily synthesized in a one-pot manner from inexpensive building blocks. Depending on the concentration, either a paracyclophane-like dimer with closely stacked benzene rings or a triangular trimer is the main product of the reaction. The macrocycles exhibit fluorescence in solution as well as in the solid state with maxima that are red-shifted with decreasing size of the macrocyclic ring and are observed at wavelengths from 590 (tetramer in solution) to 700 nm (dimer in the solid state). Chirality dictates the differential absorption and emission of circularly polarized light by these molecules. The ECD and CPL effects are particularly strong for the trimer, which is characterized by relatively large dissymmetry factors gabs =±2.8×10-3 at 531 nm and glum =±2.3×10-3 at 580 nm in n-hexane, being at the same time highly luminescent (Φfl =13.7 %). Despite the small chromophore, the circularly polarized brightness BCPL of 2.3 dm3 mol-1 cm-1 is comparable to values reported for other classes of established CPL emitters in the visible region, such as expanded helicenes or larger π-conjugated systems.

Chiral and Structural Polymorphism of Fibril Architectures of Homologous Lysozymes.

Amyloid fibrils are fascinating and complex structures with the multilayered chiral organization. Using the multimodal methodology, including VCD, ECD, cryo-EM, and TEM, we characterized in detail different levels of organization (secondary structure/protofilament/mesoscopic structure) of amyloid fibrils prepared from proteins highly homologous in the structure (hen egg white and human lysozymes). Our results demonstrate that small changes in the native protein structure or preparation conditions translate into significant differences in the handedness and architecture of the formed fibrils at various levels of their complexity. In particular, fibrils of hen egg white and human lysozymes obtained in vitro at the same preparation conditions, possess different secondary structure, protofilament twist and ultrastructure. Yet, formed fibrils adopted a relatively similar mesoscopic structure, as observed in high-resolution 3D cryo-EM, scarcely used up to now for fibrils obtained in vitro in denaturing condition. Our results add to other puzzling experiments implicating the indeterministic nature of fibril formation.

A Unique and Stable Polyproline I Helix Sorted out from Conformational Equilibrium by Solvent Polarity.

Polyproline I helical structures are often considered as the hidden face of their most famous geminal sibling, Polyproline II, as PPI is generally spotted only within a conformational equilibrium. We designed and synthesized a stable Polyproline I structure exploiting the striking tendency of (S)-indoline-2-carboxylic acid to drive the peptide bond conformation toward the cis amide isomer, when dissolved in polar solvents. The cooperative effect of only four amino acidic units is sufficient to form a preferential structure in solution. We shed light on this rare secondary structure with a thorough analysis of the spectroscopic and chiroptical properties of the tetramer, supported by X-ray crystallography and computational studies.

Electronic Circular Dichroism Imaging (ECDi) Casts a New Light on the Origin of Solid-State Chiroptical Properties.

Solid-state ECD (ss-ECD) spectra of a model microcrystalline solid, finasteride, dispersed into a KCl pellet were recorded by using the synchrotron radiation source at the Diamond B23 beamline. Scanning a surface of 36 mm2 with a step of 0.5 mm, we measured a set of ECD imaging (ECDi) spectra very different from each other and from the ss-ECD recorded with a bench-top instrument (1 cm2 area). This is due to the anisotropic part of the ECD (ACD), which averages to zero in solution or on a large number of randomly oriented crystallites, but can otherwise be extremely large. Two-way singular value decomposition (SVD) analysis, through experimental and simulated TDDFT spectra, disclosed that the measured and theoretical principal components are in line with each other. This finding demonstrates that the observed isotropic ss-ECD spectrum is governed by the anisotropy of locally oriented crystals. It also introduces a new quality for ss-ECD measurements and opens a new future for probing and mapping chiral materials in the solid state such as active pharmaceutical ingredients (APIs).

Study on the Effect of Geometrical Parameters of a Hexagonal Trigger on Energy Absorber Performance Using ANN.

Thin-walled structures are commonly used as energy absorbers in motor vehicles. Their function is to protect the structural components of vehicles and to absorb energy completely during collisions up to 20 km/h. This paper focuses on maintaining crush axiality during research. To verify the numerical analyses, physical specimens were made and then subjected to dynamic crushing. Force and shortening values as well as high-speed camera images were used for data analysis. Through time-lapse shots, plastic deformation within the crush initiator was observed. Such detailed analysis allowed the determination of the influence of hexagonal triggers in the form of notches on the post-buckling progressive analysis. In this paper, neural networks were used to examine the importance of each variable. Data from numerical analyses were used for this purpose. Based on the analyses performed, the effects of both the width and height of the triggers on the crush load efficiency (CLE) and total efficiency (TE) ratios can be seen. The width of the crush initiator has the greatest influence on Crash-box performance. Nevertheless, increasing both the height and the width of the initiator can result in crush non-axiality and underperformance of the energy absorber.

Synthesis and Characterization of Bis[(R or S)-N-1-(X-C6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]-Λ/Δ-cobalt(II) (X = H, p-CH3O, p-Br) with Symmetry- and Distance-Dependent Vibrational Circular Dichroism Enhancement and Sign Inversion.

The enantiopure Schiff bases (R or S)-N-1-(X-C6H4)ethyl-2-hydroxy-1-naphthaldimine {X = H [(R or S)-HL1], p-CH3O [(R or S)-HL2], and p-Br [(R- or S)-HL3]} react with cobalt(II) acetate to give bis[(R or S)-N-1-(X-C6H4)ethyl-2-oxo-1-naphthaldiminato-κ2N,O]-Λ/Δ-cobalt(II) {X = H [Λ/Δ-Co-(R or S)-L1], p-CH3O [Λ/Δ-Co-(R or S)-L2], and p-Br [Λ/Δ-Co-(R or S)-L3]} (1-3), respectively. Induced Λ and Δ chirality originates at the metal center of the C2-symmetric molecule in pseudotetrahedral geometry. Differential scanning calorimetry analyses explored the thermal stability of the complexes, which undergo reversible phase transformation from crystalline solid to isotropic liquid phase for 1 and 3 but irreversible phase transformation for 2. Like other cobalt(II) complexes, compounds 1-3 exhibit a continuous ensemble of absorption and circular dichroism bands, which span from the UV to IR region and can be collected into a superspectrum. Infrared vibrational circular dichroism (IR-VCD) spectra witness the coupling between Co2+-centered low-lying electronic states and ligand-centered vibrations. The coupling produces enhanced and almost monosignate VCD spectra, with both effects being mode-dependent in terms of the A or B symmetry (in the C2 point group) and distance from the Co2+ core.

Enantioselective Gel Phase Synthesis of Metal-Organic Materials.

We report the asymmetric synthesis of homochiral metal-organic materials (MOMs) in chiral gels from achiral components. The enantioselectivity of MOMs depends on the chirality of the gel, whereas the synthesis performed in solution phase and achiral gels resulted in conglomerates.

Base-Catalyzed, Solvent-Free Synthesis of Rigid V-Shaped Epoxydibenzo[b,f][1,5]diazocines.

A novel method for the synthesis of epoxydibenzo[b,f][1,5]diazocines exhibiting a V-shaped molecular architecture is reported. The unique approach is based on unprecedented base-catalyzed, solvent-free autocondensation and cross-condensation of fluorinated o-aminophenones. The structure of the newly synthesized diazocines was confirmed independently by X-ray analysis and chiroptical methods. The rigidity of the diazocine scaffold allowed for the separation of the racemate into single enantiomers that proved to be thermally stable up to 140 °C. Furthermore, the inertness of the diazocine scaffold was demonstrated by performing a series of typical transformations, including transition metal-catalyzed reactions, proceeding without affecting the bis-hemiaminal subunit.

New camptothecin derivatives for generalized oncological chemotherapy: Synthesis, stereochemistry and biology.

Derivatives of SN38 were synthesized that were either monosubstituted at C-5 or C-9 or disubstituted at both C-5 and C-9. Substitution to C-5 led to the generation of pairs of diastereomers (2c-2 h) in a one-pot reaction and was readily separable by HPLC. The absolute configurations of C-5 were established by electronic circular dichroism experiments. Compounds were tested in vitro against human cancer cell lines as well as a normal cell line. The impact of compounds 2a-2j on cancer cells is significant and the IC50 values against the normal cell line are several times higher than that of SN38. Using the Mannich reaction we obtained a new innovative group of derivatives with unique biological properties that preserves the high cytotoxicity in cancer cells and eliminates the acute toxicity to non-neoplastic cells, which can be considered a breakthrough in chemotherapy with the use of topoisomerase I inhibitors from the camptothecin family.

Fluorescent Molecular Cages with Sucrose and Cyclotriveratrylene Units for the Selective Recognition of Choline and Acetylcholine.

The synthesis of four fluorescent diastereoisomeric molecular cages containing cyclotriveratrylene and sucrose moieties connected via the naphthalene linkers is reported. These diastereoisomers were found to be selective and efficient receptors for acetylcholine and choline. Compound P-5a has a better affinity for choline over acetylcholine, while cage M-5a exhibits a higher association constant for acetylcholine over choline. The highest selectivity value was observed for compound M-5a (KACh/KCh = 3.1). Cages P-5a, P-5b, M-5a, and M-5b were fully characterized by the advanced NMR techniques, and ECD spectroscopy was supported by DFT calculations. The binding constants Ka of these receptors were determined by fluorescence titration experiments in acetonitrile.

Influence of Corrugated Web Geometry on Mechanical Properties of I-Beam: Laboratory Tests.

This paper presents the results of experimental investigations performed on beams with corrugated webs. The aim of the research was to determine the effect of the geometric parameters of the sinusoidal web on the behavior of I-beams subjected to four-point bending. Special attention was paid to the effects of web thickness and wave geometry on the deflection of beams. The obtained failure modes of particular test samples are presented. Reference has also been made to the determined standard load capacities based on Annex D of the EC3 standard. In order to compare the performance of beams with corrugated webs, the results for beams with flat webs of the same thickness of web sheets are also presented.

A Holistic Approach to Determining Stereochemistry of Potential Pharmaceuticals by Circular Dichroism with ß-Lactams as Test Cases.

This paper's main objective is to show that many different factors must be considered when solving stereochemical problems to avoid misleading conclusions and obtain conclusive results from the analysis of spectroscopic properties. Particularly in determining the absolute configuration, the use of chiroptical methods is crucial, especially when other techniques, including X-ray crystallography, fail, are not applicable, or give inconclusive results. Based on various ß-lactam derivatives as models, we show how to reliably determine their absolute configuration (AC) and preferred conformation from circular dichroism (CD) spectra. Comprehensive CD analysis, employing both approaches, i.e., traditional with their sector and helicity rules, and state-of-the-art supported by quantum chemistry (QC) calculations along with solvation models for both electronic (ECD) and vibrational (VCD) circular dichroism ranges, allows confident defining stereochemistry of the ß-lactams studied. Based on an in-depth analysis of the results, we have shown that choosing a proper chiroptical method/s strictly depends on the specific case and certain structural features.

Isolation and Self-Association Studies of Beta-Lactoglobulin.

The aim of this study was to investigate isolated ß-lactoglobulin (ß-LG) from the whey protein isolate (WPI) solution using the column chromatography with SP Sephadex. The physicochemical characterization (self-association, the pH stability in various salt solutions, the identification of oligomeric forms) of the protein obtained have been carried out. The electrophoretically pure ß-LG fraction was obtained at pH 4.8. The fraction was characterized by the matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/TOF MS) technique. The use of the HCCA matrix indicated the presence of oligomeric ß-LG forms, while the SA and DHB matrices enabled the differentiation of A and B isoforms in the sample. The impact of sodium chloride, potassium chloride, ammonium sulfate, and sodium citrate in dispersion medium on ß-LG electrophoretic stability in solution was also studied. Type of the dispersion medium led to the changes in the isoelectric point of protein. Sodium citrate stabilizes protein in comparison to ammonium sulfate. Additionally, the potential of capillary electrophoresis (CE) with UV detection using bare fused capillary to monitor ß-LG oligomerization was discussed. Obtained CE data were further compared by the asymmetric flow field flow fractionation coupled with the multi-angle light scattering detector (AF4-MALS). It was shown that the ß-LG is a monomer at pH 3.0, dimer at pH 7.0. At pH 5.0 (near the isoelectric point), oligomers with structures from dimeric to octameric are formed. However, the appearance of the oligomers equilibrium is dependent on the concentration of protein. The higher quantity of protein leads to the formation of the octamer. The far UV circular dichroism (CD) spectra carried out at pH 3.0, 5.0, and 7.0 confirmed that ß-sheet conformation is dominant at pH 3.0, 5.0, while at pH 7.0, this conformation is approximately in the same quantity as α-helix and random structures.

Steroidal Molecular Rotors with 1,4-Diethynylphenylene Rotators: Experimental and Theoretical Investigations Toward Seeking Efficient Properties.

Properly designed molecular rotors with sizable stators and a fast-moving rotator could provide efficient building blocks for amphidynamic crystals. Herein, we report the synthesis of steroidal compounds 1, 2, and 3 and their deuterated analogues 1D, 2D, and 3D envisioned to work as molecular rotors. The obtained compounds were characterized by attenuated total reflection-infrared, Raman, and circular dichroism (CD) spectroscopy measurements. The interpretation of spectra was supported by theoretical calculations using density functional theory methods. The analysis of the most characteristic bands confirmed different molecular dynamics of the rotors investigated. Angle-dependent polarized Raman spectra showed the crystallinity of some samples. Electronic CD (ECD) spectra of compounds 1-3 and their relevant deuterated analogues 1D-3D are identical. The increase of the band intensity with lowering the temperature shows that the equilibrium is shifted to the thermodynamically most stable conformer. ECD spectra simulated at the TDFFT level of theory for compound 3 were compared with experimental results. It was proved that conformer 3a, with a torsion angle of +50°, exhibits the best agreement with the experimental results. Simulated vibrational CD and IR spectra for conformer 3a and its deuterated analogue 3Da also display good agreement with experimental results. In light of our comprehensive investigations, we evidenced that steroidal compounds 1, 2, and 3 can work as molecular rotors.

Novel Potent Muscarinic Receptor Antagonists: Investigation on the Nature of Lipophilic Substituents in the 5- and/or 6-Positions of the 1,4-Dioxane Nucleus.

A series of novel 1,4-dioxane analogues of the muscarinic acetylcholine receptor (mAChR) antagonist 2 was synthesized and studied for their affinity at M1-M5 mAChRs. The 6-cyclohexyl-6-phenyl derivative 3b, with a cis configuration between the CH2N+(CH3)3 chain in the 2-position and the cyclohexyl moiety in the 6-position, showed pKi values for mAChRs higher than those of 2 and a selectivity profile analogous to that of the clinically approved drug oxybutynin. The study of the enantiomers of 3b and the corresponding tertiary amine 33b revealed that the eutomers are (2S,6S)-(-)-3b and (2S,6S)-(-)-33b, respectively. Docking simulations on the M3 mAChR-resolved structure rationalized the experimental observations. The quaternary ammonium function, which should prevent the crossing of the blood-brain barrier, and the high M3/M2 selectivity, which might limit cardiovascular side effects, make 3b a valuable starting point for the design of novel antagonists potentially useful in peripheral diseases in which M3 receptors are involved.

Chiral Diketopyrrolopyrrole-Helicene Polymer With Efficient Red Circularly Polarized Luminescence.

Chiral diketopyrrolopyrrole (DPP)-helicene polymers were synthesized to develop efficient red circularly polarized (CP) light emitters. These original chiral dyes display intense electronic circular dichroism (ECD) and CP luminescence (CPL) in the far-red spectral region owing to the presence of excitonic coupling between achiral DPPs within the chiral environment of the polymeric structure. This work affords an interesting example illustrating the potential of π-conjugated helical polymers for chiral optoelectronic applications.

Gigantelline, gigantellinine and gigancrinine, cherylline- and crinine-type alkaloids isolated from Crinum jagus with anti-acetylcholinesterase activity.

Three undescribed Amarylidaceae alkaloids, named gigantelline, gigantellinine and gigancrinine, were isolated from Crinum jagus (syn. = Crinum giganteum) collected in Senegal, together with the already known sanguinine, cherylline, lycorine, crinine, flexinine and the isoquinolinone derivative hippadine. Gigantelline, gigantellinine and gigancrinine were characterized as 4-(6,7-dimethoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-yl)-phenol, its 7-O-demethyl-5ꞌ-hydroxy-4ꞌ-methoxy derivative and 5,6a,7,7a,8a,9-hexahydro-6,9a-ethano[1,3]dioxolo[4,5-j]oxireno[2,3-b]phenanthridin-9-ol, respectively, by using spectroscopic (1D and 2D 1H and 13C NMR and HRESIMS) and chemical methods. Their relative configuration was assigned by NOESY NMR spectra and NMR calculations, while the absolute configuration was assigned using electronic circular dichroism (ECD) experiments and calculations. Sanguinine, cherylline, crinine, flexinine, and the isoquinolinone hippadine, were isolated for the first time from C. jagus. Cherylline, gigantellinine, crinine, flexinine and sanguinine inhibited the activity of AChE in a dose-dependent manner, and inhibition by sanguinine was remarkably effective (IC50 = 1.83 ±â€¯0.01 µM). Cherylline and hippadine showed weak cytotoxicity at 100 µM.