Spatial structure of felodipine dissolved in DMSO by 1D NOE and 2D NOESY NMR spectroscopy

Influence of Solvent Polarity on the Conformer Ratio of Bicalutamide in Saturated Solutions: Insights from NOESY NMR Analysis and Quantum-Chemical Calculations

The study presents a thorough and detailed analysis of bicalutamide's structural and conformational properties. Quantum chemical calculations were employed to explore the conformational properties of the molecule, identifying significant energy differences between conformers. Analysis revealed that hydrogen bonds stabilise the conformers, with notable variations in torsion angles. Conformers were classified into 'closed' and 'open' types based on the relative orientation of the cyclic fragments. NOE spectroscopy in different solvents (CDCl3 and DMSO-d6) was used to study the conformational preferences of the molecule. NOESY experiments provided the predominance of 'closed' conformers in non-polar solvents and a significant presence of 'open' conformers in polar solvents. The proportions of open conformers were 22.7 ± 3.7% in CDCl3 and 59.8 ± 6.2% in DMSO-d6, while closed conformers accounted for 77.3 ± 3.7% and 40.2 ± 6.2%, respectively. This comprehensive study underscores the solvent environment's impact on its structural behaviour. The findings significantly contribute to a deeper understanding of conformational dynamics, stimulating further exploration in drug development.

NMR-Verified Dearomatization of 5,7-Substituted Pyrazolo[1,5-a]pyrimidines

Tetrahydropyrazolo[1,5-a]pyrimidine (THPP) is an attractive scaffold for designing biologically active compounds. The most obvious way to obtain such compounds is to reduce pyrazolopyrimidines with complex hydrides, because the pyrimidine ring is reduced in the preference over the pyrazole ring. The presence of substituents at positions five and seven of pyrazolo[1,5-a]pyrimidines complicates the set of reaction products but makes it more attractive for medicinal chemistry because four possible stereoisomers can be formed during reduction. However, the formation of only syn-isomers has been described in the literature. This article is the first report on the formation of anti-configured isomers along with syn-isomers in the reduction of model 5,7-dimethylpyrazolo[1,5-a]pyrimidine, which was confirmed by NMR. The bicyclic core in the syn-configuration was shown to be conformationally stable, which was used to estimate the long-range interproton distances using NOESY data. At the same time, long-range dipole-dipole interactions corresponding to a distance between protons of more than 6 Å were first registered and quantified. In turn, the bicyclic core in the trans-configuration represents a conformationally labile system. For these structures, an analysis of conformations observed in solutions was carried out. Our results indicate the significant potential of trans-configured tetrahydropyrazolo[1,5-a]pyrimidines for the development of active small molecules. While possessing structural lability due to the low energy of the conformational transition, they have the ability to adjust to the active site of the desired target.

Structural Identification and Antioxidant Activity of Loach Protein Enzymatic Hydrolysates

Loach, rich in nutrients, such as proteins, amino acids, and mineral elements, is being gradually favored by consumers. Therefore, in this study, the antioxidant activity and structural characteristics of loach peptides were comprehensively analyzed. The loach protein (LAP) with a molecular weight between 150 and 3000 Da was graded by ultrafiltration and nanofiltration processes, which exhibited excellent scavenging activity against DPPH radical (IC50 2.91 ± 0.02 mg/mL), hydroxyl radical (IC50 9.95 ± 0.03 mg/mL), and superoxide anion radical (IC50 13.67 ± 0.33 mg/mL). Additionally, LAP was purified by gel filtration chromatography, and two principal components (named as LAP-I and LAP-II) were isolated. A total of 582 and 672 peptides were identified in LAP-I and LAP-II, respectively, through structural analysis. The XRD results revealed that LAP-I and LAP-II had an irregular amorphous structure. The 2D-NMR spectroscopy results suggested that LAP-I had a compact stretch conformation in the D₂O solution, while LAP-II had a folded conformation. Overall, the study results suggested that loach peptide could be a potential antioxidant agent and might provide valuable information for chain conformation and antioxidant mechanism research further.

Exploring the Conformational Equilibrium of Mefenamic Acid Released from Silica Aerogels via NMR Analysis

This study examines the influence of mefenamic acid on the physical and chemical properties of silica aerogels, as well as its effect on the sorption characteristics of the composite material. Solid state magic angle spinning nuclear magnetic resonance (MAS NMR) and high-pressure ¹³C NMR kinetic studies were conducted to identify the presence of mefenamic acid and measure the kinetic rates of CO₂ sorption. Additionally, a high-pressure T₁-T₂ relaxation-relaxation correlation spectroscopy (RRCOSY) study was conducted to estimate the relative amount of mefenamic acid in the aerogel's pores, and a high-pressure nuclear Overhauser effect spectoscopy (NOESY) study was conducted to investigate the conformational preference of mefenamic acid released from the aerogel. The results indicate that mefenamic acid is affected by the chemical environment of the aerogel, altering the ratio of mefenamic acid conformers from 75% to 25% in its absence to 22% to 78% in the presence of aerogel.

Investigation of the Spatial Structure of Flufenamic Acid in Supercritical Carbon Dioxide Media via 2D NOESY

The search for new forms of already known drug compounds is an urgent problem of high relevance as more potent drugs with fewer side effects are needed. The trifluoromethyl group in flufenamic acid renders its chemical structure differently from other fenamates. This modification is responsible for a large number of conformational polymorphs. Therefore, flufenamic acid is a promising structural modification of well-known drug molecules. An effective approach in this field is micronization, employing "green" supercritical fluid technologies. This research raises some key questions to be answered on how to control polymorphic forms during the micronization of drug compounds. The results presented in this work demonstrate the ability of two-dimensional nuclear Overhauser effect spectroscopy to determine conformational preferences of small molecular weight drug compounds in solutions and fluids, which can be used to predict the polymorphic form during the micronization. Quantitative analysis was carried out to identify the conformational preferences of flufenamic acid molecules in dimethyl sulfoxide-d6 medium at 25 °C and 0.1 MPa, and in mixed solvent medium containing supercritical carbon dioxide at 45 °C and 9 MPa. The data presented allows predictions of the flufenamic acid conformational preferences of poorly soluble drug compounds to obtain new micronized forms.

Conformational Screening of Arbidol Solvates: Investigation via 2D NOESY

Understanding of the nucleation process's fundamental principles in saturated solutions is an urgent task. To do this task, it is necessary to control the formation of polymorphic forms of biologically active compounds. In certain cases, a compound can exist in a single polymorphic form, but have several solvates which can appear in different crystal forms, depending on the medium and conditions of formation, and show different pharmaceutical activity. In the present paper, we report on the analysis of Arbidol conformational preferences in two solvents of different polarities-deuterated chloroform and dimethyl sulfoxide-at 25 °C, using the 2D NOESY method. The Arbidol molecule has various solvate forms depending on the molecular conformation. The method based on the nuclear Overhauser effect spectroscopy was shown to be efficient in the analysis of complex heterocyclic compounds possessing conformation-dependent pseudo-polymorphism. It is one of the types of polymorphism observed in compounds forming crystal solvates. Combined use of NMR methods and X-ray data allowed determining of conformer populations of Arbidol in CDCl₃ and DMSO-d₆ which were found to be 8/92% and 37/63%, respectively. The preferred conformation in solution is the same that appears in stable crystal solvates of Arbidol.

Structures Controlled by Entropy: The Flexibility of Strychnine as Example

To study the flexibility of strychnine, we performed molecular dynamics simulations with orientational tensorial constraints (MDOC). Tensorial constraints are derived from nuclear magnetic resonance (NMR) interaction tensors, for instance, from residual dipolar couplings (RDCs). Used as orientational constraints, they rotate the whole molecule and molecular parts with low rotational barriers. Since the NMR parameters are measured at ambient temperatures, orientational constraints generate conformers that populate the whole landscape of Gibbs free energy. In MDOC, structures are populated that are not only controlled by energy but by the entropy term TΔS of the Gibbs free energy. In the case of strychnine, it is shown that ring conformers are populated, which has not been discussed in former investigations. These conformer populations are not only in accordance with RDCs but fulfill nuclear Overhauser effect (NOE)-derived distance constraints and ³J_HH couplings as well.

The Role of Hidden Conformers in Determination of Conformational Preferences of Mefenamic Acid by NOESY Spectroscopy

Mefenamic acid has been used as a non-steroidal anti-inflammatory drug for a long time. However, its practical use is quite limited due to a number of side effects on the intestinal organs. Conformational polymorphism provides mefenamic acid with unique properties regarding possible modifications obtained during the micronization process, which can improve pharmacokinetics and minimize side effects. Micronization can be performed by decompression of supercritical fluids; methods such as rapid expansion of the supercritical solution have proven their efficiency. However, this group of methods is poorly applicable for compounds with low solubility, and the modification of the method using a pharmaceutically suitable co-solvent may be useful. In our case, addition of only 2 mol% dimethyl sulfoxide increased the solubility remarkably. Information on the conformational state may be critically important for carrying out micronization. In this work, structural analysis and estimate of conformational preferences of mefenamic acid in dimethyl sulfoxide-d6 (at 25 °C and 0.1 MPa) and in a mixed solvent supercritical carbon dioxide + dimethyl sulfoxide-d6 (45 °C, 9 MPa) were performed based on nuclear Overhauser effect spectroscopy. Results show changes in the conformation fractions depending on the medium used. The importance of allowing for hidden conformers in estimating the conformational state was demonstrated in the analysis. Obtained results may be useful for improving micronization parameters.

Co(III)-tetra(4-sulfonatophenyl)porphyrin complexes with bidentate ligands in aqueous buffer media

The processes of hydrophilic Co(III)-tetra(4-sulfonatophenyl)porphyrin supramolecular assembly with 4,4-bipyridyl in aqueous buffer media have been studied by UV-vis, 1D and 2D 1H NMR-spectroscopy. In the case of 1,4-diazabicyclo[2.2.2]octane, pyrazine and piperazine in aqueous solutions, no assembly was observed. Interactions of the hydrophilic Co(III)-tetraarylporphyrin with ionic micelles (cationic surfactants with different alkyl tail lengths) in buffer media were investigated. These studies were performed by the UV-vis, 1D NOESY-spectroscopy and dynamic lightscattering (DLS) methods. The metalloporphyrins were incorporated into the hydrophobic part of micelles, which led to Co(III) reduction to Co(II) in the Co-porphyrinate composition. The rate of Co(III) reduction accompanied by detachment of additional ligands coordinated on Co(III)-porphyrins or disruption of supramolecular dimers and depends on the surfactant concentration and nature. The results obtained indicate the possibility of creating supramolecular porphyrin-based assemblies with the preprogrammed lifetime (from several hours to several days) and could be used in the creation of host-guest systems for recognition, selective binding and the prolonged release of bioactive substrates as the means in the designing of biomimetic systems with effective binding affinities to heterocycles, DNA base pairs and RNA.

Fabrication and characterization of spearmint oil loaded nanoemulsions as cytotoxic agents against oral cancer cell

Spearmint oil (SMO), a commonly used essential oil for oral care products, possesses various interesting functions, especially for anticancer property. However, the application of SMO for cancer treatment is limited due to water insoluble. In the present study, nanoemulsions, which have been widely accepted as dosage forms for poorly water-soluble drugs, were selected as candidate carriers for SMO to inhibit oral cancer cell. The nanoemulsions were fabricated using phase inversion temperature method. The factors affecting formation and properties of nanoemulsions including type and amount of surfactants, oil loading and ratio of SMO to virgin coconut oil (VCO) were investigated. Among the surfactants used, the nanoemulsions containing polyoxyethylene castor oil derivatives (Kolliphor®EL; PCO35, Cremophor®RH40; PCO40, Eumulgin®CO60; PCO60) and polyoxyethylene sorbitan fatty acid esters (PSF80) showed 100% creaming after temperature cycling test indicating excellent physical stability while those containing PCO40 demonstrated more transparency and better physical stability. With an increasing amount of PCO40, the droplet size tended to decrease and was in the nano-size range (<1000 nm) after increasing to more than 5% (w/w). SMO-VCO loading also influenced on the droplet size. At 5% (w/w) PCO40, the maximum SMO-VCO loading of 25% (w/w) to attain nanoemulsions was observed. Moreover, the composition of oils had an impact on size of emulsions. The transparent nanoemulsions were only prepared in the range of SMO-VCO from 40:60 to 80:20, suggesting the optimum ratio of SMO to surfactant and the composition of oils were the critical factors for formation of nanoemulsions. NMR study disclosed that the interaction between PCO40 with both VCO and SMO should be a possible stabilization mechanism. Furthermore, the SMO-VCO nanoemulsions exhibited significant cytotoxic effect against oral carcinoma (KON) cell line using MTT assay. The finding, therefore, revealed the good feasibility of SMO-VCO nanoemulsions as novel carriers for treating of oral cancer.

N-Confused porphyrins: complexation and 1H NMR studies

The complexation of 2-aza-21-carba-tetraphenylporphyrin and 2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrin with nickel and zinc acetates in organic solvents has been investigated by UV-Vis spectroscopy and ¹H NMR.