Filtering the NMR Spectra of Complex Mixtures through Polymer‐Mediated Paramagnetic Spin Relaxation

Filtering the NMR Spectra of Mixtures by Coordination to Paramagnetic Cu2

The paramagnetic spin relaxation (PSR) filter allows the selective NMR signal suppression of components in mixtures according to their complexation ability to a paramagnetic ion. It relies on the faster relaxation of nuclei in paramagnetic environments and thus is complementary to classical diffusion and relaxation filters. So far, the PSR filter has established Gd³⁺ as the sole PSR agent, restricting the paramagnetic filtering repertoire. Herein, we present Cu²⁺ as a robust PSR agent with characteristic filtering properties. While Gd³⁺ depends on unspecific ion-pair interactions with anionic components, Cu²⁺ stands out for filtering species via ordered coordination complexes. An evaluation of the paramagnetic effect of Cu²⁺ over more than 50 small molecules and polymers has unveiled different sensitivities to Cu²⁺ (especially high for pyridines, diamines, polyamines, and amino alcohols) and precise filtering conditions for mixtures (¹H, COSY, and HMQC) that were challenged with a test bed of commercial drugs. The advantage of integrating Cu²⁺ and Gd³⁺ for the stepwise PSR filtering of complex mixtures is also shown.

Metabolomic tools used in marine natural product drug discovery

Introduction: The marine environment is a very promising resource for natural product research, with many of these reaching the market as new drugs, especially in the field of cancer therapy as well as the drug discovery pipeline for new antimicrobials. Exploitation for bioactive marine compounds with unique structures and novel bioactivity such as the isoquinoline alkaloid; trabectedin, the polyether macrolide; halichondrin B, and the peptide; dolastatin 10, requires the use of analytical techniques, which can generate unbiased, quantitative, and qualitative data to benefit the biodiscovery process. Metabolomics has shown to bridge this understanding and facilitate the development of new potential drugs from marine sources and particularly their microbial symbionts.Areas covered: In this review, articles on applied secondary metabolomics ranging from 1990-2018 as well as to the last quarter of 2019 were probed to investigate the impact of metabolomics on drug discovery for new antibiotics and cancer treatment.Expert opinion: The current literature review highlighted the effectiveness of metabolomics in the study of targeting biologically active secondary metabolites from marine sources for optimized discovery of potential new natural products to be made accessible to a R&D pipeline.

Matrix-assisted DOSY

The analysis of mixtures by NMR spectroscopy is challenging. Diffusion-ordered NMR spectroscopy enables a pseudo-separation of species based on differences in their translational diffusion coefficients. Under the right circumstances, this is a powerful technique; however, when molecules diffuse at similar rates separation in the diffusion dimension can be poor. In addition, spectral overlap also limits resolution and can make interpretation challenging. Matrix-assisted diffusion NMR seeks to improve resolution in the diffusion dimension by utilising the differential interaction of components in the mixture with an additive to the solvent. Tuning these matrix-analyte interactions allows the diffusion resolution to be optimised. This review presents the background to matrix-assisted diffusion experiments, surveys the wide range of matrices employed, including chromatographic stationary phases, surfactants and polymers, and demonstrates the current state of the art.