Combined In-Solution Fragment Screening and Crystallographic Binding-Mode Analysis with a Two-Domain Hsp70 Construct

Heat shock protein 70 (Hsp70) isoforms are key players in the regulation of protein homeostasis and cell death pathways and are therefore attractive targets in cancer research. Developing nucleotide-competitive inhibitors or allosteric modulators, however, has turned out to be very challenging for this protein family, and no Hsp70-directed therapeutics have so far become available. As the field could profit from alternative starting points for inhibitor development, we present the results of a fragment-based screening approach on a two-domain Hsp70 construct using in-solution NMR methods, together with X-ray-crystallographic investigations and mixed-solvent molecular dynamics simulations. The screening protocol resulted in hits on both domains. In particular, fragment binding in a deeply buried pocket at the substrate-binding domain could be detected. The corresponding site is known to be important for communication between the nucleotide-binding and substrate-binding domains of Hsp70 proteins. The main fragment identified at this position also offers an interesting starting point for the development of a dual Hsp70/Hsp90 inhibitor.

Chemometric analysis applied to 1 H NMR and FTIR data for a quality parameter distinction of red fruit (Pandanus conoideus, lam.) oil products

INTRODUCTION

Red fruit oil (RFO) is a natural product extracted from Pandanus conoideus Lam. fruit, a native plant from Papua, Indonesia. Recent studies indicate that RFO is popularly consumed as herbal medicine. Therefore, the quality of RFO must be assured.

OBJECTIVES

This study aimed to develop a chemometric analysis applied to 1 H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) data for important quality parameter distinction of red fruit oil (RFO), especially regarding the degree of unsaturation and the amount of free fatty acids (FFA).

MATERIALS AND METHODS

Forty samples consisting of one crude RFO, thirty-three commercial RFOs, and three oils as blends, including olive oil, virgin coconut oil, and black seed oil, were analysed by 1 H NMR and FTIR spectroscopy. After appropriate preprocessing of the spectra, principal component analysis (PCA) and partial least squares regression (PLSR) were used for model development.

RESULTS

The essential signals for modelling the degree of unsaturation are the signal at δ = 5.37-5.27 ppm (1 H NMR) and the band at 3000-3020 cm-1 (FTIR). The FFA profile represents the signal at δ = 2.37-2.20 ppm (1 H NMR) and the band at 1680-1780 cm-1 (FTIR). PCA allows the visualisation grouping on both methods with > 98% total principal component (PC) for the degree of unsaturation and > 88% total PC for FFA values. In addition, the PLSR model provides an acceptable coefficient of determination (R2 ) and errors in calibration, prediction, and cross-validation.

CONCLUSION

Chemometric analysis applied to 1 H NMR and FTIR spectra of RFO successfully grouped and predicted product quality based on the degree of unsaturation and FFA value categories.

Isolation and Characterization of Galloylglucoses Effective against Multidrug-Resistant Strains of Escherichia coli and Klebsiella pneumoniae

The search for new antibiotics against multidrug-resistant (MDR), Gram-negative bacteria is crucial with respect to filling the antibiotics development pipeline, which is subject to a critical shortage of novel molecules. Screening of natural products is a promising approach for identifying antimicrobial compounds hosting a higher degree of novelty. Here, we report the isolation and characterization of four galloylglucoses active against different MDR strains of Escherichia coli and Klebsiella pneumoniae. A crude acetone extract was prepared from Paeonia officinalis Linnaeus leaves, and bioautography-guided isolation of active compounds from the extract was performed by liquid–liquid extraction, as well as open column, flash, and preparative chromatographic methods. Isolated active compounds were characterized and elucidated by a combination of spectroscopic and spectrometric techniques. In vitro antimicrobial susceptibility testing was carried out on E. coli and K. pneumoniae using 2 reference strains and 13 strains hosting a wide range of MDR phenotypes. Furthermore, in vivo antibacterial activities were assessed using Galleria mellonella larvae, and compounds 1,2,3,4,6-penta-O-galloyl-β-d-glucose, 3-O-digalloyl-1,2,4,6-tetra-O-galloyl-β-d-glucose, 6-O-digalloyl-1,2,3,4-tetra-O-galloyl-β-d-glucose, and 3,6-bis-O-digalloyl-1,2,4-tri-O-galloyl-β-d-glucose were isolated and characterized. They showed minimum inhibitory concentration (MIC) values in the range of 2–256 µg/mL across tested bacterial strains. These findings have added to the number of known galloylglucoses from P. officinalis and highlight their potential against MDR Gram-negative bacteria.

Tracing the origin of paracetamol tablets by near-infrared, mid-infrared, and nuclear magnetic resonance spectroscopy using principal component analysis and linear discriminant analysis

Most drugs are no longer produced in their own countries by the pharmaceutical companies, but by contract manufacturers or at manufacturing sites in countries that can produce more cheaply. This not only makes it difficult to trace them back but also leaves room for criminal organizations to fake them unnoticed. For these reasons, it is becoming increasingly difficult to determine the exact origin of drugs. The goal of this work was to investigate how exactly this is possible by using different spectroscopic methods like nuclear magnetic resonance and near- and mid-infrared spectroscopy in combination with multivariate data analysis. As an example, 56 out of 64 different paracetamol preparations, collected from 19 countries around the world, were chosen to investigate whether it is possible to determine the pharmaceutical company, manufacturing site, or country of origin. By means of suitable pre-processing of the spectra and the different information contained in each method, principal component analysis was able to evaluate manufacturing relationships between individual companies and to differentiate between production sites or formulations. Linear discriminant analysis showed different results depending on the spectral method and purpose. For all spectroscopic methods, it was found that the classification of the preparations to their manufacturer achieves better results than the classification to their pharmaceutical company. The best results were obtained with nuclear magnetic resonance and near-infrared data, with 94.6%/99.6% and 98.7/100% of the spectra of the preparations correctly assigned to their pharmaceutical company or manufacturer.

Bioinspired Ion Pairs Transforming Papaverine into a Protic Ionic Liquid and Salts

Microbial, mammalian, and plant cells produce and contain secondary metabolites, which typically are soluble in water to prevent cell damage by crystallization. The formation of ion pairs, for example, with carboxylic acids or mineral acids, is a natural blueprint to maintain basic metabolites in solution. Here, we aim at showing whether the mostly large carboxylates form soluble protic ionic liquids (PILs) with the basic natural product papaverine resulting in enhanced aqueous solubility. The obtained PILs were characterized by 1H-15N HMBC nuclear magnetic resonance (NMR) and in the solid state using X-ray powder diffraction, differential scanning calorimetry, and dissolution measurements. Furthermore, their supramolecular pattern in aqueous solution was studied by means of potentiometric and photometrical solubility, NMR aggregation assay, dynamic light scattering, zeta potential, and viscosity measurements. Thereby, we identified the naturally occurring carboxylic acids, citric acid, malic acid, and tartaric acid, as being appropriate counterions for papaverine and which will facilitate the formation of PILs with their beneficial characteristics, like the improved dissolution rate and enhanced apparent solubility.

Distinguishing paracetamol formulations: Comparison of potentiometric "Electronic Tongue" with established analytical techniques

Fast and inexpensive analytical tools for identification of the origin of pharmaceutical formulations are important to ensure consumers safety. This study explores the potential of potentiometric multisensor systems ("electronic tongues") in this type of application. 72 paracetamol samples purchased in different countries and produced by various companies were studied via infrared spectroscopy (IR), near infrared spectroscopy (NIR), nuclear magnetic resonance spectroscopy (NMR) and multisensor system (ET). A variety of chemometric tools was applied to explore and compare the information yielded by these methods. It was found that ET is capable of distinguishing paracetamol formulations from different producers. The chemical information derived from potentiometric sensor responses has something in common with that derived from NIR and IR; however, it is orthogonal to that from NMR. ET can be a valuable tool in express quality assessment of drugs.

Assessment of inhibitory potency of antibiotics by MRI: apparent T2 as a marker of cell growth

A new method to assess the antibiotic potency by MRI has been developed. Correlating 1H NMR spectra of bacterial cultures with the extracellular parameters T2, OD600, and pH, a relationship between cell growth and T2 variations was established. T2 is influenced by chemical exchange that depends on pH, composition, and concentration of the medium. Changes in the medium from bacterial metabolism are reflected in alternating T2 values. At 17.6 T, growth curves based on T2 values were measured simultaneously of several cultures of Streptococcus vestibularis. From T2 growth curves in the presence of varying concentrations of vancomycin, the minimum inhibitory concentration of the antibiotic could be determined to be 0.33+/-0.08 microM. This value was in good agreement with the result obtained by the conventional broth microdilution. In principle, T2 growth curves can be determined on a large number of cultures simultaneously and may potentially be used as a novel tool in high through-put screening of novel anti-infective substances.

Quantitative NMR spectroscopy--applications in drug analysis

NMR spectroscopy being a primary ratio method of measurement is highly suitable to evaluate the quality of drugs. NMR spectroscopy can be used for the identification of a drug substance, the identification and quantification of impurities arising from the synthesis pathway and degradation, or residual solvents as well as the determination of the content in the assay. This review gives an overview of the application of quantitative NMR spectroscopy in International Pharmacopoeias and for licensing purposes.