Current and Future Perspectives on the Structural Identification of Small Molecules in Biological Systems

Abstract

Although significant advances have been made in recent years, the structural elucidation of small molecules continues to remain a challenging issue for metabolite profiling. Many metabolomic studies feature unknown compounds; sometimes even in the list of features identified as "statistically significant" in the study. Such metabolic "dark matter" means that much of the potential information collected by metabolomics studies is lost. Accurate structure elucidation allows researchers to identify these compounds. This in turn, facilitates downstream metabolite pathway analysis, and a better understanding of the underlying biology of the system under investigation. This review covers a range of methods for the structural elucidation of individual compounds, including those based on gas and liquid chromatography hyphenated to mass spectrometry, single and multi-dimensional nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry and includes discussion of data standardization. Future perspectives in structure elucidation are also discussed; with a focus on the potential development of instruments and techniques, in both nuclear magnetic resonance spectroscopy and mass spectrometry that, may help solve some of the current issues that are hampering the complete identification of metabolite structure and function.

The integration of LC‐MS and NMR for the analysis of low molecular weight trace analytes in complex matrices

“…A majority of metabolites from the profiling experiments, are structurally unknown thus the identification of these unknown metabolites is the primary challenge in metabolomics. Metabolite identification is challenging because the metabolome is comprised of small molecules with different physicochemical properties and with a wide range of concentrations, thus a single analytical platform is not sufficient for its analysis and because many platforms do not provide sufficient information to characterize markers of interest …”

Metabolômica: Definições, Estado-Da-Arte E Aplicações Representativas

“…Menos frequentemente, podem ser encontradas aplicações utilizando infravermelho por transformada de Fourier (FT-IR, do inglês, Fourier transform infrared spectroscopy), que demonstra grande potencial por ser uma técnica de elucidação estrutural de baixo custo, simples e não destrutiva. 23 A NMR é uma técnica simples, robusta e abrangente, que requer pouca ou nenhuma manipulação de amostra, podendo ser analisadas amostras biológicas intactas (sólidos e semi-sólidos). 24,25 Tem a vantagem de precisar de pouca quantidade de amostra e não destruir a mesma após análise, apesar de contaminá-la com solventes deuterados.…”

ChemFrag: Chemically meaningful annotation of fragment ion mass spectra

“…In particular, it is applied in metabolomics, diagnostics, pharmaceutical chemistry, the discovery of signaling molecules, and in doping control. () The key technologies for the detection and identification of small molecules are mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR), whereby MS has an outstanding position because of its high sensitivity, low detection limits, speed, and diversity of its application . Furthermore, the MS system can be coupled to gas (GC‐MS) or liquid chromatography (LC‐MS) to separate complex mixture before MS analysis, eg, the analytical process by MS involves the conversion of the sample into gaseous ions, with or without fragmentation, which is then characterised by their mass to charge ratios ( m/z ) and relative abundances.…”